Exploring facet-engineered anatase nanoparticles for amplification of sensitivity in heavy metal ion detection and other applications

Abstract

TiO₂ is one of the most extensively studied nanomaterials due to its remarkable surface, catalytic, and electronic properties, which are further enhanced when synthesized with exposed facets. In this study, anatase-phase TiO₂ nanoparticles with different crystal facets were synthesized using inorganic modifiers through a hydrothermal method. The synthesized samples were characterized using various analytical techniques. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy confirmed the formation of anatase TiO₂. The crystallite size, estimated from XRD data, ranged between 1–50 nm, except for the linear straight-line method (LSLM), which exhibited a higher value. Growth preference, texture coefficient and Raman data and structural analysis verified the facet formation. Additionally, thermogravimetric analysis (TGA) revealed enhanced thermal stability of the samples. Photocatalytic studies demonstrated that {001}-faceted and {101}/{001} co-faceted TiO₂ achieved complete degradation of Congo Red (CR) dye within 30 min, significantly outperforming {101}-faceted TiO₂ (69.36% degradation). Scavenging experiments confirmed that ˙OH radicals played the dominant role in CR degradation over the {001}-faceted TiO₂. Kinetic studies based on the Langmuir–Hinshelwood model revealed apparent rate constants of 0.0202 min⁻¹ for {101}-faceted TiO₂, 0.0081 min⁻¹ for {001}-faceted TiO₂, and 0.0127 min⁻¹ for {101}/{001}-co-faceted TiO₂. Furthermore, {001}-faceted TiO₂ exhibited significant antimicrobial efficacy against Gram-positive bacteria, attributed to enhanced surface activity. Electrochemical studies revealed the superior sensing capabilities of {001}-faceted TiO₂ for Pb²⁺ ion detection, with its enhanced electroactive surface area contributing to a limit of detection (LOD) of 9.378 ppm and a limit of quantification (LOQ) of 31.162 ppm.

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Introduction

Nowadays, nanomaterials are widely valued for their exceptional properties over bulk materials. For example, nanostructured titanium dioxide (TiO₂), with its remarkable optical and electronic features, has revolutionized applications in photocatalysis, sensors, photovoltaics, and photonic devices.¹ This affordable, non-toxic, and stable semiconductor is extensively used in dye sensitized solar cells,² pollutant remediation,³ charge spreading devices,⁴ gas sensors,⁵ photocatalytic degradation, photoluminescence,⁶ bactericides,⁷ optical coatings,⁸ opto-electronic devices,⁹ electrochemistry,¹⁰ textiles¹¹ etc. TiO₂ is found predominantly in three crystalline forms: anatase, brookite, and rutile. Anatase is notable for its high catalytic efficiency, attributed to its vast surface area, minimal charge recombination, strong oxygen affinity, and broad bandgap, making it highly effective under UV light.¹² The performance of TiO₂ is influenced by its physical and chemical properties, including crystal structure, grain size, morphology, and surface characteristics, prompting interest in synthesizing TiO₂ with specific crystal structures to enhance highly photoactive facets. Different facets of a single crystal exhibit distinct properties, affecting reactivity.¹³ Anatase TiO₂, with its wide band gap, demonstrates photocatalytic activity through photogenerated electrons (e⁻) and holes (h⁺) at the surface, initiating redox reactions. However, electron–hole recombination during transport reduces carrier efficiency, with charge separation relying on trapping holes by H₂O or electrons by O₂. Surface properties, such as crystal facets, defects, and adsorbed ions, impact charge migration, making the modification of TiO₂ crystal facets a key focus.¹⁴ Moreover, TiO₂ encounters limitations such as a broad band gap, low quantum yield, and swift recombination of photogenerated charges, which constrain its visible light absorption and hinder large-scale applications. In recent years, facet engineering of TiO₂ crystals has gained prominence as an effective strategy to boost photocatalytic efficiency.¹⁵

Various methods, including sputtering,¹⁶ aerosol pyrolysis,¹⁷ MOCVD,¹⁸ electrodeposition,¹⁹ spray pyrolysis,²⁰ sol–gel,²¹ and hydrothermal synthesis,²² have been employed to fabricate TiO₂ nanostructured thin films. Among these, hydrothermal synthesis is particularly favored for its simplicity, cost-effectiveness, and ability to produce well-aligned nanostructures with a high surface area. It also allows for the straightforward synthesis of single-crystalline materials.²³ Hydrothermal or solvothermal techniques typically operate at temperatures below 1000 °C, offering energy efficiency compared to alternative approaches like chemical vapor deposition, which often require higher temperatures. These methods provide precise control over the morphology and crystallinity of TiO₂, making them ideal for photocatalysis and sensing applications.²⁴

For TiO₂, the primary low-index facets are {101}, {001}, and {100}. Among these, the {001} facet of anatase TiO₂ is particularly reactive due to its high surface energy (0.90 J m⁻²), which exceeds that of the {100} (0.53 J m⁻²) and {101} (0.44 J m⁻²) facets, making it a key player in photocatalytic applications.²⁵ However, due to its thermodynamic instability, the {001} facet is rarely exposed in large quantities, with most natural and synthesized TiO₂ crystals predominantly showing the {101} facet. The reactivity of the {001} facet, characterized by low atomic coordination and active surface oxygen atoms, facilitates efficient dissociative adsorption of reactant molecules, making it ideal for photocatalytic processes such as the degradation of organic pollutants including various dyes.²⁶ Among these, Congo Red (CR) is frequently selected in photocatalytic studies due to its highly stable complex aromatic azo structure, which makes it persistent in water and resistant to natural degradation. Its metabolites, including benzidine, are toxic, exhibiting carcinogenic and mutagenic properties, and can trigger allergic reactions, increase chemical oxygen demand in water bodies, and even contribute to infertility. These characteristics make CR considerably more difficult to degrade, establishing it as a rigorous benchmark for evaluating photocatalytic performance.^27,28 Recent research has focused on manipulating TiO₂ crystal facets to enhance photocatalytic performance, particularly by increasing the exposure of {001} facets, which are essential for trapping holes as oxidative sites. However, some studies have also reported that {101} facets exhibit higher photocatalytic activity than {001} facets in certain applications.²⁹

In addition to organic pollutants, the increasing levels of heavy metal contaminants have drawn significant public and scientific concern due to their toxicity, bioaccumulation, and persistence in ecosystems.³⁰ Heavy metals such as lead (Pb²⁺), cadmium (Cd²⁺), and mercury (Hg²⁺) pose severe health risks, including neurological disorders, organ damage, and carcinogenic effects.³¹ In recent years, electrochemical sensors have gained widespread attention in chemical and biological studies due to their high sensitivity, simplicity, cost-effectiveness, and reliability in detecting trace pollutants.³² Various analytical techniques, including atomic absorption spectroscopy (AAS),³³ inductively coupled plasma mass spectrometry (ICP-MS),³⁴ and X-ray fluorescence (XRF)³⁵ are commonly used for the detection and quantification of heavy metals. However, these methods often require expensive instrumentation, complex sample preparation, and time-consuming preconcentration procedures.³⁶ Among electrochemical techniques, anodic stripping voltammetry (ASV) has emerged as a powerful and widely applied method for detecting heavy metal ions in water. ASV offers high sensitivity, accuracy, low cost, and the ability to detect multiple metal ions simultaneously.³⁷ The technique involves an initial preconcentration step, where metal ions accumulate on an electrode surface, followed by a stripping step, during which the deposited metals are reoxidized, producing measurable current signals proportional to metal ion concentration.³⁸ This makes ASV a highly efficient, rapid, and environmentally friendly approach for monitoring heavy metal contamination in water sources, offering advantages over traditional detection techniques.³⁹

Beyond their application in photocatalysis and electrochemical sensing, TiO₂ nanoparticles have also demonstrated significant antimicrobial properties. The antimicrobial mechanism primarily involves direct interaction with bacterial cell walls, leading to structural changes, increased membrane permeability, and eventual cell death.⁴⁰

In this study, anatase-phase TiO₂ nanoparticles with various exposed crystal facets were synthesized using inorganic modifiers such as NH₄Cl, NH₄SO₄, and HF. The synthesized TiO₂ samples were thoroughly characterized using a range of techniques, and the influence of facet modification on their photocatalytic, antimicrobial, and electrochemical properties was further investigated. The photocatalytic degradation of Congo Red (CR) dye was evaluated, alongside antimicrobial activity, to assess the material's effectiveness in environmental pollutant removal and microbial inhibition. Additionally, electrochemical sensors for the detection of Pb²⁺ ions were fabricated using the synthesized TiO₂, targeting heavy metal sensing applications. These investigations aim to enhance the understanding of how facet modification can tune TiO₂'s properties, thereby improving its performance in environmental remediation and sensing applications.

Materials and methods

Materials and equipment

Tetrabutyl orthotitanate (purity 98%) was acquired from Tokyo Chemical Industry Co. Ltd, Japan. Ammonium chloride (purity 99%), hydrofluoric acid (purity 48%), sulfuric acid (purity 99%), ammonia (purity 25%) and isopropanol were acquired from Merck, Germany. Crystallographic analysis was performed using a Rigaku XRD instrument with Cu Kα X-rays (λ = 1.5406 Å) at 40 kV and 50 mA, with a cooling temperature of 23 °C. Functional groups were analyzed via FT-IR spectroscopy using an IR-Prestige 21 spectrometer, scanning from 400 to 4000 cm⁻¹ with a resolution of 4 cm⁻¹ and 30 scans. Thermal analysis was conducted using STA equipment in a nitrogen atmosphere, ranging from 50 °C to 800 °C. Structural and elemental characterization was done using a JEOL JSM-7610F field emission scanning electron microscope (FESEM) with integrated energy-dispersive X-ray spectroscopy (EDX) capabilities at 25 kV and SEM, EVO-18, Carl Zeiss, Germany machine.

Experimental methods

Synthesis of different crystal plane faceted TiO₂. For the synthesis of {101}-faceted TiO₂, 2 g of tetrabutyl orthotitanate (TBOT) was dispersed in a solution composed of 15 mL DI water and 15 mL isopropanol. Subsequently, 0.2 g of NH₄Cl was introduced into the reaction mixture, which was stirred and ultrasonicated to achieve a uniform dispersion. The prepared suspension was then transferred to a Teflon-lined autoclave, sealed, and heated at 180 °C for 24 hours under hydrothermal conditions. Upon completion of the reaction, the solid product was recovered through filtration, followed by extensive washing with DI water and a single wash with ethanol to eliminate residual impurities. Finally, the cleaned product was dried in an oven at 105 °C, yielding the desired {101}-faceted TiO₂. Fig. S1 shows the schematic depiction of the synthesis procedure of {101}-faceted TiO₂.

For the synthesis of {001}-faceted TiO₂, 8.33 mL of TBOT was mixed with 1 mL of HF in a dry Teflon-lined autoclave and heated at 180 °C for 24 hours under hydrothermal conditions. Upon the reaction's completion, the product was recovered through filtration, followed by extensive washing with water and a single wash with ethanol to remove residual impurities. To eliminate any remaining fluorine species, the product was further treated with an aqueous NaOH solution, followed by additional washing with deionized water. Finally, the purified material was dried in an oven at 105 °C, yielding {001}-faceted TiO₂. Fig. S2 shows the schematic depiction of the synthesis procedure of {001}-faceted TiO₂.

For the synthesis of {101}/{001} co-faceted TiO₂, 2 g of TBOT was dissolved in a mixture of 15 mL deionized water and 15 mL isopropanol. Subsequently, 0.5 g (NH₄)₂SO₄ was added to the reaction mixture, followed by stirring and ultrasonication to ensure uniform dispersion. The subsequent steps mirrored the synthesis of {101}-faceted TiO₂. Fig. S3 shows the schematic depiction of the synthesis procedure of {101}/{001} co-faceted TiO₂.

The (NH₄)₂SO₄ used to prepare the {101}/{001} co-faceted TiO₂ was synthesized by adding diluted H₂SO₄ dropwise to an NH₃ solution under continuous stirring. The addition of H₂SO₄ was carefully monitored until the solution reached a neutral pH of 7. The resulting solution was then heated to 50 °C to facilitate water evaporation. Once crystals formed, the remaining water was removed by drying the crystals in a vacuum oven at 50 °C. The crystals were subsequently crushed using a mortar and pestle to obtain a powder.

Photocatalytic assessment. The photocatalytic assessment was conducted using Congo Red (CR) dye as a model pollutant, with a 40 mL solution of 10 ppm CR dye and a sample weight of 0.05 g. A 500 W SEN TAI JM-500 halogen lamp was used as the visible light source, with the sample placed 0.14 m beneath the lamp. The temperature in the irradiation chamber was maintained at 25 °C using a cooling water circulation system. The concentration of the dye was measured using a Hitachi U-910 UV-vis spectrometer, after the assessment. The degradation percentage was calculated using the following formula:⁴¹Here, C₀ is the concentration at the beginning, C_t is the concentration of the synthesized sample at a particular time, t.

Scavenging experiments were carried out using 2-propanol (isopropyl alcohol) and ethylenediaminetetraacetic acid (EDTA) as scavengers for hydroxyl radicals (˙OH) and photogenerated holes (h⁺), respectively. In each experiment, 10 mL of the scavenger solution was added to 40 mL of 10 ppm CR dye containing 0.05 g of the catalyst, followed by halogen irradiation for 30 min. The reusability of the catalyst was evaluated under identical conditions over five consecutive cycles.⁴² After each cycle, the catalyst was decanted, washed three times with water, dried at 60 °C for 6 h, and reused with a fresh dye solution.

Antimicrobial activity. The synthesized samples were tested for antimicrobial efficacy against two Gram-positive bacteria (L. monocytogenes ATCC 13932, S. aureus ATCC 6538), two Gram-negative bacteria (S. abony NCTC 6017, E. coli ATCC 25922), and a fungal strain, C. albicans ATCC 10342. For the assay, 50 mg of each sample was dissolved in distilled water containing 2% Tween 20 (Promega, USA). Chloramphenicol served as the positive control for antibacterial activity, while Azoxystrobin was used as the positive control for antifungal activity. The experiment was carried out using the agar-well diffusion method, where a fresh microbial culture was evenly spread onto the agar surface. Using an sterile cotton bud, 6 mm diameter wells were carefully created on the agar plate. The prepared sample solutions were then introduced into each well to assess antimicrobial effectiveness. The plates were stored at 4 °C for 3 hours to ensure uniform dispersion of the sample particles, then incubated at 37 °C for 24 hours, after which the inhibition zones were observed and their diameters measured.

Electrochemical experiment. Electrochemical experiments were conducted using the CS300 (Corrtest, China) with a three-electrode system: Pt as the counter electrode, Ag/AgCl as the reference, and a modified glassy carbon (GC) electrode as the working electrode. The modification of the GC electrode was carried out using a mixture of {001}-modified TiO₂ sample, carbon black (CB) as a conducting agent, polyvinylidene fluoride (PVDF) as a binder, and N-methyl pyrrolidone (NMP) as a volatile solvent. The composition of the mixture was as follows: 70% TiO₂ sample, 20% CB, and 10% PVDF. NMP was used to dissolve PVDF and facilitate uniform mixing.

Results

Characterization

The XRD diffractogram of the synthesized TiO₂ samples, shown in Fig. 1, was compared with the standard ICDD database for anatase (card no: #00-021-1272). The anatase phase, belonging to the tetragonal crystal system with the space group I41/amd (141), is characterized by prominent peaks at 2θ values of 25.28° (1 0 1), 37.80° (0 0 4), 48.05° (2 0 0), and 53.89° (1 0 5). The synthesized samples exhibited slight variations: the {101}-faceted TiO₂ showed peaks at 25.35°, 37.73°, 47.84°, and 54.40°; the {001}-faceted TiO₂ at 25.21°, 37.90°, 47.92°, and 53.75°; and the {101}/{001} co-faceted TiO₂ at 25.30°, 37.89°, 47.89°, and 54.11°. These results demonstrate strong agreement with the standard anatase phase, confirming the successful synthesis of the desired crystal structure.

Fig. 1 XRD diffractogram of the synthesized TiO₂ samples.

An evaluation of the crystal structure was performed by determining lattice parameters, crystallite size, dislocation density, and microstrain using eqn (E1)–(E5), with outcomes tabulated in Table 1.

Table 1 Crystallographic parameters of the synthesized TiO₂ samples

Sample	Lattice parameters, Å	Size of crystallites, D (nm)	Dislocation density, δ (10^15 lines per m^2)	Microstrain, ε	Crystallinity index
{101}	a = b = 3.78, c = 9.53	6.74	2.2	0.99	0.70
{001}	a = b = 3.79, c = 9.49	15.12	4.37	0.56	1.02
{101}/{001}	a = b = 3.80, c = 9.49	5.47	3.34	1.01	1.21

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Various crystallite parameters, such as size of the crystallite, intrinsic strain, stress, and energy density can be computed using XRD data by using different XRD models, comprising Scherrer's model, modified Williamson–Hall methods, the Monshi–Scherrer (M–S) model, the size-strain plot (SSP), and the Halder–Wagner (H–W) model. Each of these models considers different factors that affect the diffraction pattern, including peak broadening due to instrumental effects, internal strain, and stress, along with the isotropic or anisotropic nature of the crystal lattice. These factors significantly influence the XRD parameters owing to imperfections in the crystal structure, such as point defects, triple junctions, dislocations, grain boundaries, and stacking faults. These defects typically contribute to peak broadening and variations in lattice strain, which directly impact the accuracy of the crystallite size estimation. Thus, the application of multiple models allows for a more in-depth and precise calculation of the size of the crystallite and other parameters.⁴³ In Scherrer's model, the average size of the crystallite is estimated using the equation, crystallite size, and displayed in Table 1. The parameters obtained from other models are summarized in Table 2, while the corresponding plots are shown in Fig. S4–S10, with the corresponding equations available elsewhere.⁴⁴

Table 2 Estimated crystallite property parameters of the synthesized TiO₂ samples

Name of model		Crystallite size, D (nm); strain, ε; stress, σ (N m^−2); energy density, μ (J m^−3)
		{101}	{001}	{101}/{001}
Williamson–Hall model	UDM	ε = 0.0032	ε = −0.0023	ε = 0.0018
		D = 7.62	D = 5.52	D = 5.68
	USDM	σ = 6.533 × 10^8	σ = −4.633 × 10^8	σ = 3.76 × 10^8
		D = 7.62	D = 5.52	D = 5.68
	UDEDM	μ = 1.04 × 10^6	μ = −5.22 × 10^6	μ = 3.43 × 10^5
		D = 7.62	D = 5.52	D = 5.68
M–S model		D = 6.59	D = 10.93	D = 10.93
SSP		D = 6.25	D = 5.35	D = 4.9
		ε = 0.0028	ε = −0.004	ε = 0.0014
H–W model		D = 45.05	D = 38.61	D = 35.09
		ε = 0.005	ε = −0.007	ε = 0.002
S–S model		D = 7.70	D = 22.36	D = 5.78

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Growth preference and texture coefficient are two key parameters used to assess whether a crystalline material exhibits growth in a specific exposed plane. Growth preference provides insights into the favorable growth direction along a specific crystallographic plane and can be estimated using the normalized intensity of that plane, as calculated with eqn (E6) and (E7). Here, negative values indicate a lower preference for growth on the specific plane, whereas positive values suggest that growth on this specific plane is thermodynamically stable. In contrast, the texture coefficient (T_c) is utilized to examine the actual growth direction of the crystallographic plane. Estimation of the texture coefficient was done using the peak intensities associated with the (101), (004), (200), and (105) planes, as recorded from the XRD data, employing eqn (E8). When T_c(hkl) surpasses 1, it indicates that crystallites are more prevalently oriented in the (hkl) direction.

Table 3 presents the preferred growth values for the synthesized TiO₂ samples, while Table 4 shows the texturing behavior of the synthesized TiO₂ samples. For the {101}-faceted TiO₂, positive preferred growth values were observed for the (004) and (105) planes, suggesting a strong tendency for growth along the {001} and {101} directions, respectively. However, the texture coefficient indicates that texturing predominantly occurs along the {101} direction, as evidenced by the higher T_c value for the (105) plane, while the (004) plane shows a significantly lower T_c value. This correlation supports the conclusion that the sample predominantly exposes the (101) crystallographic direction, confirming the alignment of crystallites along this direction. In contrast, for the {001}-faceted TiO₂, a positive preferred growth value was found only for the (004) plane, and the texture coefficient for this plane exceeded 1. These findings confirm that the sample is mainly exposed along the {001} direction. Additionally, the {101}/{001}-co-faceted TiO₂ exhibited positive preferred growth values for both the (004) and (105) planes, with notable T_c values for both planes, confirming that this sample exhibits growth along both the {101} and {001} directions.

Table 3 Growth preference in the synthesized TiO₂ samples

Sample	Plane	Growth preference
{101}	101	−0.38
	004	0.46
	200	−0.04
	105	0.85
{001}	101	−0.14
	004	0.46
	200	−0.08
	105	−0.01
{101}/{100}	101	−0.30
	004	1.27
	200	−0.50
	105	0.66

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Table 4 Texture coefficient in the synthesized TiO₂ samples

Sample	Plane (hkl)	Texture coefficient, (Tc)	Observation
{101}	101	0.6500	101 direction texturing
	004	1.1616
	200	0.7928
	105	1.3956
{001}	101	0.8679	001 direction texturing
	004	1.3232
	200	0.8571
	105	0.9517
{101}/{100}	101	0.6850	101 and 001 direction texturing
	004	1.6152
	200	0.4511
	105	1.2487

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FT-IR is a highly effective and widely employed method for analyzing materials by identifying the functional groups embedded in their structure. Fig. 2 displays the FT-IR spectra of the synthesized TiO₂ samples. Absorption in the 400–700 cm⁻¹ region, indicative of the stretching and bending vibrations of the Ti–O–Ti bond, was prominently observed in all samples, confirming its presence in the synthesized nanoparticles. Apart from this region, a peak around 1631 cm⁻¹ was detected, attributed to the O–H bending vibrations (Ti–OH). For {001}-faceted TiO₂, the absorption peaks are prominent at 423, 434, 457, 496, 556, 598, 647, and 1631 cm⁻¹, with other samples showing close proximity to these values. Similar absorption peaks to those samples have been observed in previous literature.^45,46

Fig. 2 FT-IR spectra of the synthesized TiO₂ samples.

The Raman spectra, illustrated in Fig. 3, demonstrate that all samples exhibit similar spectral profiles at approximately 144, 395, 516, and 636 cm⁻¹. The most intense peak, observed near 144 cm⁻¹, corresponds to the E_g vibrational mode of anatase. The band at 395 cm⁻¹ is attributed to the B_1g mode, while the peak at 516 cm⁻¹ results from the overlapping of the A_1g (513 cm⁻¹) and B_1g (519 cm⁻¹) modes of anatase. Additionally, the E_g mode at 636 cm⁻¹ is also evident. The E_g peak results from O–Ti–O symmetric stretching, while the B_1g and A_1g modes arise from symmetric and asymmetric O–Ti–O bending, respectively.⁴⁷ Moreover, Tian et al.⁴⁸ suggested that the {001} facet percentage can be determined by analyzing the intensity of the 144 cm⁻¹ and 516 cm⁻¹ peaks as outlined in Table 5.

Fig. 3 Raman spectra of the synthesized TiO₂ samples.

Table 5 Calculation of the percentage of {001} and {101} plane in the synthesized TiO₂ samples

Sample	Intensity of the 144 cm^−1 peak	Intensity of the 514 cm^−1 peak	Percentage of {001}	Percentage of {101}
{101}	19 639.96	1094.11	5.57	94.43
{001}	18 162.15	6443.15	35.48	64.52
{101/001}	28 353.15	1446.65	5.10	94.90

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The heat response behavior of the synthesized TiO₂ particles was assessed by performing thermal weight loss analysis. The thermogram (Fig. 4) for the synthesized TiO₂ samples, heated from 50 °C to 800 °C under a controlled atmosphere, illustrates the weight-loss events occurring during the heating process. Both {101}-faceted and {001}-faceted TiO₂ samples exhibited a similar trend in the TGA curve, with nearly identical mass losses of 6.52% and 6.74%, respectively. In contrast, {101}/{001}-co-faceted TiO₂ demonstrated a slightly lower mass loss of 4.67%. The weight loss below 120 °C was attributed to the elimination of physiosorbed water molecules, while the loss above 120 °C was due to the evaporation of surface-adsorbed hydroxyl groups and the removal of unreacted residues such as F⁻ and Cl⁻, which may account for the increased weight loss in {101} and {001} faceted TiO₂ compared to pure TiO₂. A similar weight loss pattern has been observed in previous studies.^49–51

Fig. 4 Thermal weight loss of the synthesized TiO₂ samples.

Fig. 5 illustrates the surface morphology of the synthesized {101}-faceted (Fig. 5A), {001}-faceted (Fig. 5B) and {101}/{001}-co-faceted (Fig. 5C) TiO₂ samples. A large amount of aggregated nanosheets was observed at both lower and higher magnifications for the {001}-faceted TiO₂. This observation verifies the formation of {001} facets, of a shape similar to those reported in previous literature.¹⁴ In contrast, the {101} faceted TiO₂ particles are densely aggregated and distorted in shape. Although the structure is not clearly understood, previous studies suggest that the shape of this sample could correspond to nanowires. One such particle, appearing as a nanowire, is highlighted in the zoomed-in figure.⁵² Similarly, the morphology of the {101}/{001} co-faceted TiO₂ samples was not clearly defined, as both low and high magnification images revealed densely aggregated, distorted, and irregular shapes. The particle sizes of the {101} and {001}-faceted TiO₂ nanoparticles were found to be similar, with average dimensions of 120.106 nm and 80.833 nm, respectively, as analyzed using ImageJ for image processing and Origin for data visualization (Fig. S11). Although these two samples showed no significant size differences, the {101}/{001} co-faceted TiO₂ demonstrated a substantially larger average particle size of 1027.06 nm. This notable increase is likely due to particle aggregation or enhanced growth caused by interactions between the two facets during the synthesis process.

Fig. 5 FESEM image of the synthesized (A) {101}-faceted, (B) {001}-faceted, and (C) {101}/{001} co-faceted TiO₂ samples.

The EDX spectrum analysis for the {101} and {001}-faceted TiO₂ nanoparticles is shown in Fig. S12a and b. The EDX results validate the exclusive presence of titanium (Ti) and oxygen (O) in both samples, with their corresponding peaks in the spectrum at the expected locations. According to the weight percentage analysis, the {101}-faceted TiO₂ contained 30.98% oxygen and 69.02% titanium, while the {001}-faceted TiO₂ showed 30.05% oxygen and 69.95% titanium, reflecting similar chemical profiles. The results align well with the anticipated compositions, providing evidence of the successful synthesis of the TiO₂ nanoparticles.

Photocatalytic degradation of dye

The photocatalytic performance of the TiO₂ samples was assessed using CR as a model dye over a 30 min period, with the degradation percentages presented in Fig. 6(a). Both {001}-faceted and {101}/{001}-co-faceted TiO₂ samples achieved complete degradation of CR (100%) within the allotted time, while the {101}-faceted TiO₂ demonstrated a lower degradation efficiency of 69.36%. The enhanced photocatalytic activity of the {001}-faceted and {101}/{001}-co-faceted TiO₂ can be attributed to the superior surface reactivity and larger surface area of the {001} facet.⁵³

Fig. 6 (a) CR degradation percentage, (b) scavenging analysis, (c) reusability, and (d) kinetics of the photocatalytic degradation of the synthesized TiO₂ samples.

Fig. 6(b) illustrates the degradation percentages obtained from the scavenging tests using IPA and EDTA. In the presence of isopropanol (IPA), an ˙OH radical quencher, the degradation efficiency of {001}- and {101}/{001}-faceted TiO₂ decreased sharply from 100% to 12.7% and 49.88%, respectively, confirming that ˙OH radicals are the dominant oxidative species generated on the {001} surface. Likewise, addition of EDTA, a hole (h⁺) scavenger, reduced the degradation efficiency of {001} and {101}/{001} TiO₂ to 28.81% and 20.33%, respectively.

The reusability of the photocatalysts was evaluated over five consecutive degradation cycles, as shown in Fig. 6(c). The {101}-faceted TiO₂ exhibited the best performance with 79.90% degradation efficiency even after the fifth cycle, while the {001}-faceted TiO₂ maintained 55.84%. In contrast, the {101}/{001}-co-faceted TiO₂ initially showed the highest degradation efficiency during the first four cycles, with nearly comparable performance in each run; however, its activity declined in the last few cycles, reaching only 42.69% degradation efficiency.

Fig. 6(d) depicts the kinetics of CR dye degradation over the synthesized TiO₂ samples, fitted using the Langmuir–Hinshelwood model according to the equation:^54,55

ln(C₀/C_t) = K_appt

where C₀ and C_t are the initial and time-dependent concentrations, respectively, and K_app is the apparent first-order rate constant. A linear relationship was obtained by plotting ln(C₀/C_t) versus irradiation time (t), and the slope corresponds to K_app. The calculated rate constants (visualized in Fig. 6(d)) were 0.0202 min⁻¹ for {101}-faceted TiO₂, 0.0081 min⁻¹ for {001}-faceted TiO₂, and 0.0127 min⁻¹ for {101}/{001}-co-faceted TiO₂.

Antimicrobial activity

The antimicrobial activity of the synthesized TiO₂ samples, including {101}-faceted TiO₂ (T1), {001}-faceted TiO₂ (T2), and {101}/{001}-cofaceted TiO₂ (T3), was assessed against two Gram-positive bacteria, two Gram-negative bacteria, and a fungal strain. Chloramphenicol served as the positive control for antibacterial activity, while Azoxystrobin was used as the positive control for antifungal activity.

As shown in the results (Fig. 7), both {101} and {001}-faceted TiO₂ demonstrated notable antimicrobial activity against Gram-positive bacteria but exhibited inadequate activity against Gram-negative bacteria and the fungal strain, with inhibition zones falling below the detection limit of 6 mm. Among the tested samples, {001}-faceted TiO₂ (T2) exhibited the highest antibacterial activity against L. monocytogenes, with an inhibition zone of 11.5 ± 0.50 mm, followed by comparable activity against S. aureus (11.5 ± 0.50 mm). In contrast, {101}-faceted TiO₂ (T1) showed slightly lower antibacterial activity, with inhibition zones of 9.2 ± 0.91 mm against S. aureus and 8.6 ± 0.40 mm against L. monocytogenes. These results suggest that both {101} and {001}-faceted TiO₂ samples possess significant antimicrobial efficacy against Gram-positive bacteria under the tested conditions. However, the {101}/{001} co-faceted TiO₂ (T3) failed to exhibit adequate antimicrobial activity against any of the tested microorganisms. In contrast, the positive controls (Chloramphenicol for bacteria and Azoxystrobin for fungi) displayed excellent antimicrobial activity, confirming the validity of the assay. Table 6 shows the inhibition zone diameters, summarizing the antimicrobial activity of the tested samples against the selected microbes.

Fig. 7 Evaluation of antimicrobial properties of the synthesized TiO₂ samples against (A) S. aureus, (B) L. monocytogenes, (C) E. coli, (D) S. abony, and (E) C. albicans.

Table 6 Antimicrobial activity of the synthesized TiO₂ samples

Sample name	Name of tested microorganisms, diameter of zone of inhibition (mm)
	Gram-positive		Gram-negative		Fungus
	S. aureus	L. monocytogenes	E. coli	S. abony	C. albicans
a <6 mm = no significant antimicrobial activity was observed.
{101}-faceted TiO2	9.2 ± 0.91	8.6 ± 0.40	<6^a	<6^a	<6^a
{001}-faceted TiO2	11.2 ± 0.76	11.5 ± 0.50	<6^a	<6^a	<6^a
{101}/{001}co-faceted TiO2	<6^a	<6^a	<6^a	<6^a	<6^a
Positive control	15.9 ± 2.69	15.2 ± 0.75	17.9 ± 4.25	17.2 ± 0.89	16.3 ± 1.10

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Electrochemical analysis

To evaluate the electrochemical performance of the {001}-modified GC electrode, cyclic voltammetry was conducted at the potential range of −0.5 to 1.0 V with a scan rate of 100 mV s⁻¹ using 2.5 µM [Fe(CN)₆]^3−/4− as a redox probe containing 0.1 M NaCl as the supporting electrolyte, illustrated in Fig. 8(a). The {001}-modified electrode exhibited an anodic peak potential (E_p.a) of 0.24704 V and a cathodic peak potential (E_p.c) of 0.10115 V, resulting in a peak-to-peak separation (ΔE) of 145.89 mV. This value was significantly lower than that of the bare GC electrode [E_p.a = 0.37406 V, E_p.c = 0.08920 V, and ΔE = 284.86 mV]. The reduced ΔE suggests enhanced electron transfer kinetics. A comparable effect has been reported in the literature for the G/PANI nanocomposite-modified electrodes.⁵⁶ Moreover, the {001}-modified electrode exhibited a higher anodic peak current (I_p.a = 97.28 µA cm⁻²) and cathodic peak current (I_p.c = 53.80 µA cm⁻²) compared to the bare GC electrode (I_p.a = 38.90 µA cm⁻², I_p.c = 37.01 µA cm⁻²). This variation in both potential and current can be attributed to the surface modification of the GC electrode, which enhances its electrochemical activity and charge transfer efficiency.

Fig. 8 (a) CV of the bare GC electrode and {001}-faceted TiO₂ modified GC electrode at 2.5 µM [Fe(CN)₆]^3−/4−. (b) ASV of the {001}-faceted TiO₂ modified GC electrode at different scan rate ranges from 10–140 mV using 5 ppm Pb²⁺ solution. (c) Relationship between the current and square root of the scan rate measured in 5 ppm Pb²⁺ solution. (d) ASV of Pb²⁺ at different concentrations maintaining a scan rate of 20 mV, at a GC modified electrode. (e) Relationship between the current and concentration of Pb²⁺ measured at 20 mV scan rate, 1–10 ppm concentration range. (f) ASV of the repeatability test using 0.01 ppm Pb²⁺ solution multiple times.

The effect of scan rate is crucial in the sensing process as it provides insight into the nature of mass transport at the interface.⁵⁷ To study this, anodic stripping voltammetry (ASV) was conducted within a scan rate range of 10 to 120 mV s⁻¹, using a fixed concentration of 5 ppm Pb²⁺, as shown in Fig. 8(b). The results show that the peak current increases with the scan rate, while the potential shifts in the positive direction, indicating the irreversibility of the reaction at the electrode surface. A linear relationship (y = 0.2351x + 0.1506) with a regression coefficient of 0.8867, obtained from the plot of peak current versus the square root of the scan rate (Fig. 8(c)), suggests that the mass transport at the electrode interface is diffusion-controlled.

The effectiveness of the fabricated sensor for detecting Pb²⁺ was assessed using ASV within the concentration range of 1 to 10 ppm, under the experimental conditions of a 160 s deposition time, deposition voltage of −1.2 V, scan range of −0.8 to 0.5 V, and a scan rate of 20 mV s⁻¹ (displayed in Fig. 8(d)). ASV works by applying a higher negative potential than the reduction potential, allowing metal ions to deposit on the electrode surface. In this experiment, the reduction potential was found to be around +0.07 V, thus the deposition was performed at −1.2 V, fixed after several variations. A linear relationship (y = 0.032x + 0.6453) with a regression coefficient of 0.8519 showed good linearity between 1 and 10 ppm, with peak current increasing linearly with Pb²⁺ concentration (Fig. 8(e)). This behavior stems from the presence of a moiety that reacted actively with the targeted analyzed ions.⁵⁸ After deposition, the reduced metals were stripped from the electrode surface within a potential range of −0.8 V to 0.5 V. The limit of detection (LOD) was calculated using the slope and standard deviation (LOD = 3 × SD/slope), yielding a value of 9.378 ppm for Pb²⁺ detection. The limit of quantification (LOQ) was calculated similarly (LOQ = 10 × SD/slope), with the resulting value being 31.262 ppm.

The repeatability of the electrode's response to Pb²⁺ ions was evaluated through multiple ASV experiments at the concentration of 0.01 ppm (shown in Fig. 8(f)). The results show consistent peak current values with no significant variation, confirming its reliability and accuracy in the detection of Pb²⁺ ions.

Discussion

TiO₂ has garnered significant attention as one of the most extensively studied metal oxides, owing to its exceptional surface, electronic, and catalytic properties. These attributes are further enhanced when specific crystal facets are exposed, which influence its reactivity, making it a promising candidate for various applications.⁵⁹ In this study, TiO₂ nanoparticles were synthesized with exposed {101}, {001}, and {101}/{001} facets to explore their structural and photocatalytic properties. The successful formation of anatase-phase TiO₂ was confirmed through XRD, FTIR and Raman analysis. Crystallite size calculations using various XRD models revealed that the crystallite sizes of all samples, except LSLM, fall within the range of 0–50 nm.

Growth preference and texture coefficient analyses verified that the synthesized TiO₂ nanoparticles were formed with specific exposed facets. For the {101}-faceted TiO₂, the growth preference was observed on the (004) and (105) planes, reflecting a thermodynamically favored growth direction. However, the texture coefficient for the (004) plane was relatively low, suggesting minimal growth along the {001} direction, confirming that the {101} direction is the dominant exposed facet. On the other hand, {001}-faceted TiO₂ exhibited a positive growth preference value and good texture coefficient for the (004) plane, confirming the dominance of the {001} facet in the sample. The co-faceted samples, which displayed higher texture coefficients for both the (105) and (004) planes, were characterized by the coexistence of both {101} and {001} facets. Raman analysis also confirmed growth on specific facets, as the {101}-faceted sample has 94.43% growth in the {101} direction, whereas the {001}-faceted sample has 35.48% growth in the {001} direction. However, for the {101}/{001} co-faceted sample, Raman analysis indicated growth only along the {101} direction, despite growth preference and texture coefficient analyses confirming the presence of both facets. This discrepancy may be attributed to the sample's morphology, where the particles exhibit significant aggregation, leading to cluster formation and an increase in particle size, as evidenced by the histogram analysis, which recorded a large particle size of 1027.6 nm. The larger particle size causes volume expansion, increasing the vibrational amplitude of neighboring molecules due to a rise in the mean square relative displacement. As a result, the Raman shift increases, particularly for the E_g peaks at 144 cm⁻¹, disrupting the accurate estimation of the {001} facet percentage. A similar pattern is also seen in previous literature.⁶⁰

The morphological features of the synthesized TiO₂ nanoparticles were further examined using FESEM. The {001}-faceted samples displayed a nanosheet-like structure, while the {101}-faceted samples exhibited an aggregated nanowire structure, consistent with previous findings.^14,52 These distinct morphologies are consistent with the crystallographic preferences observed in the XRD and texture coefficient analysis, underscoring the influence of facet engineering on the structural properties of TiO₂ nanoparticles.

TiO₂ nanoparticles have demonstrated versatility in a wide range of applications, including photocatalytic degradation, sensors, dye-sensitized solar cells, charge-spreading devices, photoluminescence, bactericides, optical coatings, and optoelectronic devices. In this study, the synthesized TiO₂ nanoparticles were utilized for the photocatalytic degradation of CR dye, assessment of antimicrobial activity, and electrochemical sensing for Pb detection.

CR dye is a common pollutant in textile wastewater. The {001}-faceted and {101}/{001}-co-faceted TiO₂ achieved complete degradation of CR dye in just 30 min, compared to 69.36% degradation by {101}-faceted TiO₂ under identical conditions. This superior performance is attributed to the unique properties of the highly exposed {001} facets. The {001} facet is highly reactive due to its higher surface energy compared to the {101} facet. This is a result of the greater density of unsaturated bonds between penta-coordinated Ti (Ti_5C) atoms and two-fold coordinated oxygen atoms (O_2C).⁶¹ Notably, the {001} facets consist entirely of Ti_5C atoms (100%), making them fully accessible for photocatalytic reactions. In contrast, the {101} facet has only 50% Ti_5C atoms, which reduces its reactivity.⁵³ Furthermore, the Ti_5C–O_2C bonds on the {001} facet have a larger bond length (1.95 Å), making them easier to break upon reactant adsorption. This enhances the activity of titanium and oxygen atoms on the {001} surface, promoting photocatalytic reactions.⁶² Furthermore, these attributes enhance the generation of reactive oxygen species (ROS) that attack dye molecules at or near the photocatalyst surface and are mainly responsible for the degradation. In particular, the {001} facets have been shown to facilitate ˙OH radical formation owing to their lower activation energy for ˙OH generation.⁶³ This was confirmed by scavenging experiments: in the presence of isopropanol (IPA), an ˙OH radical quencher, the degradation efficiency of {001}-faceted TiO₂ dropped dramatically from 100% to 12.7%, indicating that ˙OH radicals are the dominant oxidative species. In contrast, the addition of EDTA reduced the degradation efficiency of {001} and {101}/{001} TiO₂ to 28.81% and 20.33%, respectively. These results demonstrate that ˙OH radicals play the primary role in the photocatalytic process over {001}-faceted TiO₂, while photogenerated holes also make a significant contribution. Overall, these findings establish that the {001} facet is highly effective in facilitating ROS generation, thereby accelerating CR dye degradation.

Previous studies have also demonstrated that facet-engineered TiO₂ exhibits enhanced photocatalytic activity compared to pure or commercial TiO₂. For instance, Hammud et al. reported that commercial P25 (Degussa) TiO₂ achieved only 60–90% Congo Red degradation after 60 min of UV irradiation at different catalyst dosages.⁶⁴ Lee et al. investigated the photocatalytic degradation of methylene blue using {101}/{001}-faceted TiO₂ and observed a higher activity with an apparent rate constant of 0.0527 min⁻¹.⁶⁵ Roy et al. synthesized TiO₂ via a green approach using amines and found that samples with ∼25% {101} and ∼75% {100}/{010} exposed facets exhibited 3.7 and 3.1-fold higher photocatalytic activity than Degussa P25 toward methyl orange and methylene blue, respectively.⁶⁶ Similarly, Leu et al. demonstrated that {001}-exposed TiO₂ composites showed significantly higher photocatalytic activity for methylene blue degradation under both UV and visible light irradiation,⁶⁷ while Gul et al. reported that highly {001}-faceted TiO₂ exhibited superior degradation of crystal violet and methyl orange compared to pure TiO₂.⁶⁸ In another study, John et al. employed C. odorata leaf extract for the green synthesis of N-doped {001}-faceted TiO₂, achieving ∼98% degradation of methylene blue.⁶⁹ Likewise, Kaur et al. synthesized E. cardamomum-wrapped TiO₂, where phytochemicals in the extract preferentially stabilized the {100} facets, resulting in 97% Congo Red degradation within 150 min.⁷⁰ Collectively, these findings confirm that {001}-exposed TiO₂ nanoparticles, particularly those synthesized through green or modified routes, can outperform commercial P25 and represent promising candidates for advanced oxidation processes aimed at degrading persistent pollutants and improving water quality.

In addition to photocatalytic degradation, {001}-faceted TiO₂ exhibited strong antimicrobial properties against Gram-positive bacteria, with inhibition zones of 11.5 ± 0.50 mm against L. monocytogenes and 11.5 ± 0.50 mm against S. aureus. In comparison, {101}-faceted TiO₂ showed inhibition zones of 9.2 ± 0.91 mm against S. aureus and 8.6 ± 0.40 mm against L. monocytogenes. This enhanced antibacterial activity of {001}-faceted TiO₂ is attributed to its greater reactivity, primarily due to the presence of unsaturated coordinated Ti atoms on the surface. These unsaturated Ti atoms interact readily with bacterial cell membranes, leading to membrane disruption. This disruption triggers oxidative stress, causing leakage of intracellular contents and ultimately resulting in bacterial cell death.⁴⁰ {001} Facets have 100% unsaturated coordinated Ti atoms, while {101} facets have only 50%, which accounts for the superior antimicrobial properties of {001}-faceted TiO₂. In contrast, the poor antimicrobial activity against Gram-negative bacteria may be due to the presence of an additional outer membrane, unlike Gram-positive bacteria, and a plasma membrane composed of both anionic and zwitterionic phospholipids, which reduces nanoparticle interaction and penetration.⁷¹ Similarly, C. albicans exhibits limited susceptibility because, as a eukaryotic organism, it has a thick cell wall and a complex, sugar-rich cell membrane that act as a protective barrier against nanoparticle entry.⁷²

The electrochemical properties of the {001}-modified TiO₂ electrode were also evaluated for Pb²⁺ ion detection through the fabrication of an electrochemical sensor using {001}-faceted TiO₂. CV confirmed that the modified electrode exhibited superior electrochemical efficiency compared to the bare GC electrode, as evidenced by reduced potential difference and enhanced current response, indicating improved charge transfer efficiency. ASV was employed to assess the mass transport mechanism at the electrode interface, revealing that the Pb²⁺ detection process was governed by an irreversible, diffusion-controlled reaction. The fabricated sensor demonstrated a LOD of 9.378 ppm and a LOQ of 31.162 ppm, confirming its sensitivity for Pb²⁺ detection. Table 7 shows the comparison of the electrochemical sensing performance for Pb²⁺ between the fabricated sensor and previous studies. Although the bare GC electrode showed significant improvement and detectable sensitivity toward Pb²⁺ with {001}-faceted modification, the LOD and LOQ can be further enhanced using nanocomposite-based electrodes or surface functionalization. Incorporating conductive nanomaterials (graphene,⁷³ carbon nanotubes⁷⁴), metallic nanoparticles (Bi,⁷⁵ Au⁷⁶), or MXene-⁷⁷ and MOF/COF-based⁷⁸ hybrid modifiers can substantially increase the active surface area, accelerate electron transfer, and enable effective preconcentration. For example, Zhang et al.'s MWCNT/MOF (ZIF-67)-modified GCE exhibited excellent conductivity and a high density of binding sites, achieving a LOD as low as 1 nM and an extended linear range of 1.38 nM–5 µM.⁷⁸ Surface functionalization with thiol or carboxyl groups can further improve selectivity for Pb²⁺ ions. For instance, Oliveira et al. reported ZnO nanofibers functionalized with L-cysteine for Pb²⁺ electrochemical sensing, achieving a LOD of 0.397 µg L⁻¹ within a linear range of 10–140 µg L⁻¹.⁷⁹ Fig. 9 illustrates the sensing mechanism for Pb²⁺ ion detection using the fabricated sensor. Upon applying a deposition voltage of −1.2 V, Pb²⁺ ions adsorbed onto the surface of the modified electrode and are reduced to Pb⁰. A subsequent stripping potential between −0.8 V and 0.5 V reoxidized Pb⁰ back to Pb²⁺, leading to desorption from the electrode.⁸⁰ The enhanced sensing capability of the {001}-modified TiO₂ electrode can be attributed to its high surface reactivity, which enables efficient interaction with Pb²⁺ ions. The repeatability tests further confirmed the electrode's stability and accuracy, demonstrating consistent peak current responses for multiple measurements.

Table 7 Comparison of electrochemical sensing performance for Pb²⁺ between the fabricated sensor and previous studies

Material	Method	Linear range	Limit of detection, LOD	Limit of quantification, LOQ	Ref.
Biomass-worm like nitrogen doped-carbon	DPASV	0.5–100 mg L^−1	0.2 mg L^−1	—	81
TiO2@Gum Arabic	DPV	1–10 ppm	0.56 ppm	1.68 ppm	82
MOF/EB-1	Voltammetry	0.54–1.15 ppm	0.077 ppm	—	83
BC@TiO2NPs	DPV	1 × 10^−6–10 µM	0.6268 × 10^−6 µM	—	84
Ti/TiO2	ASV	0.6–13.2 µM	140 nM	—	85
TiO2/AgCNF	SWASV	—	40.14 nM	—	86
NiWO4/MWCNT	DPV	50–450 µM	0.12 µM		87
TiON/TiO2	SWASV	10^−5–10^−1 mol L^−1	10^−5 mol L^−1	1.0 ×  10–4 mol L^−1	88
{001}-faceted TiO2	LSASV	(1–10) ppm	9.378 ppm	31.162 ppm	This study

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Fig. 9 Sensing mechanism of the {001}-modified TiO₂ sensor for Pb²⁺ ion detection.

Conclusion

In this study, anatase-phase TiO₂ nanoparticles with exposed {101}, {001}, and {101}/{001} facets were successfully synthesized using inorganic modifiers via a hydrothermal method. The photocatalytic degradation of CR dye under visible light irradiation demonstrated that {001}-faceted and {101}/{001} co-faceted TiO₂ exhibited complete degradation within 30 min, significantly outperforming {101}-faceted TiO₂. This underscores the critical role of facet engineering in optimizing TiO₂ for environmental remediation applications. Furthermore, the antimicrobial studies revealed that {001}-faceted TiO₂ demonstrated superior antibacterial efficacy against Gram-positive bacteria compared to {101}-faceted TiO₂. Moreover, {001}-faceted TiO₂ exhibited excellent electrochemical performance for Pb²⁺ ion detection, with a higher electroactive surface area of the fabricated sensor, facilitating efficient charge transfer and enhancing sensor performance. The sensor demonstrated a LOD of 9.378 ppm and a LOQ of 31.162 ppm. Overall, the findings demonstrate that {001}-faceted TiO₂ holds great promise for multifunctional applications, including environmental pollutant degradation, antibacterial treatments, and electrochemical sensing. Future research should aim to further improve sensitivity and selectivity through the incorporation of conductive nanomaterials, metal nanoparticles, or surface functionalization with thiol/carboxyl groups. Additionally, extending the work to real wastewater samples and other emerging contaminants, such as pharmaceutical residues, will strengthen the practical applicability of these materials.

Author contributions

Md. Anayet Ullah: curated and analyzed the data; wrote the manuscript. Newaz Mohammed Bahadur: visualized the whole research. Dipa Islam, Subarna Shandani dey, and Md. Farhad Ali: helped in data curation. Fataha Nur Robel and Samina Ahmed: supervised the findings of this work. Md. Sahadat Hossain: conceived and designed the study; analyzed the data; supervised the overall work and reviewed the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

Data will be made available on request.

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d5ma00760g.

Acknowledgements

The Bangladesh Council of Scientific and Industrial Research (BCSIR) is acknowledged by the authors for its financial support of research and development projects (ref. no. 39.02.0000.011.14.180.2024/1116; Date: 14.01.2025). Additionally, Md. Anayet Ullah expresses gratitude to Noakhali Science and Technology University's Department of Applied Chemistry and Chemical Engineering for supporting his MS thesis program at Noakhali, Bangladesh.

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