Insights into 3D-printed TiO₂-based architectures for photocatalytic and non-catalytic applications

Abstract

3D printing has fundamentally transformed the design and engineering of photocatalytic materials, enabling the fabrication of geometrically complex, hierarchically structured TiO₂ to overcome the critical limitations of conventional approaches. This comprehensive review highlights advancements in the 3D printing of TiO₂, with a particular emphasis on fabrication methodologies, photocatalytic activity, performance optimization strategies, and other non-catalytic functional applications. The discussion encompasses the benefits of 3D-printed TiO₂ structures, including the fabrication of complex geometries and the optimization and enhancement of material performance, while also critically addressing the persistent challenges of scalability and operational stability. Recent advancements, including the incorporation of secondary dopants, the formation of synergistic composite materials, and surface modification strategies, are evaluated for their contributions to enhanced photocatalytic efficiency. Beyond photocatalysis, we also explore multi-functional applications in optical sensors, thermal-mechanical composites, and dental-orthopedic biomaterials, highlighting TiO₂'s versatility across diverse technological domains. The unique capabilities of additive manufacturing facilitate the rational design of TiO₂ with tailored geometries and compositional complexity, positioning it as a promising platform for both laboratory-scale mechanistic studies and practical real-world remediation applications.

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1. Introduction

Accelerated industrialization and rapid urbanization have led to widespread environmental degradation, primarily due to the accumulation of complex pollutants in aqueous and atmospheric systems. Among the most concerning consequences of this growth is the release of a complex array of pollutants, including heavy metals, nitrogen and sulfur compounds, and persistent organic contaminants, which severely compromise ecosystem strength and pose substantial risks to human well-being. The development of efficient, sustainable, and economically viable pollutant remediation technologies capable of mineralizing or sequestering such contaminants remains a demanding task for contemporary environmental engineering groups. Among the various remediation approaches, photocatalysis has emerged as a highly promising strategy, with TiO₂ being one of the most extensively studied and practically viable photocatalysts.¹ TiO₂ exhibits exceptional responsiveness to UV-visible light, robust charge carrier–photon interactions, high chemical and thermal stability, hydrophilicity, non-toxicity, and cost-effectiveness, which make it a highly attractive and affordable choice for environmental remediation.^2–4 TiO₂ is a semiconductor that generates reactive oxygen species (ROS), prominently hydroxyl (˙OH⁻), superoxide (˙O₂⁻) radicals, and electron–hole charge carriers under UV light irradiation, and is responsible for the photocatalytic degradation reactions.^3–5 In addition to its well-known photocatalytic properties, TiO₂ is also used for non-catalytic functional applications. Its optical properties, chemical inertness, and mechanical strength make it suitable for photonic devices, energy conversion systems, biomedical implants, and structural materials. These applications leverage TiO₂'s multifunctional properties beyond catalysis, enhancing its versatility as a high-performance material across diverse technological domains.

In practice, one of the most significant challenges with TiO₂ (powder form) used in photocatalytic applications is maintaining its structural integrity, recovery, and reusability, as well as preventing cross-contamination (nanoparticle leaching). In conventional methods, such as dip coating and spraying, the photocatalytic rate is often low, leading to film damage from weak adhesion, non-uniform thickness, and excessive nanoparticle leaching. These limitations not only compromise the long-term efficiency and durability of the catalyst but also pose difficulties for safe recovery and recycling, thereby increasing the risk of environmental contamination and undermining the overall process's reliability. To overcome these problems, 3D printing technology offers a fresh, robust solution by enabling the production of structures with complex geometries tailored to specific environments, thereby improving structural, functional, and recovery–reuse properties.^6–8 3D printing methods, including stereolithography (SLA), digital light processing (DLP), direct ink writing (DIW), fused deposition modelling (FDM), and fused filament fabrication (FFF), coating on the selective laser melting (SLM) or selective laser sintering (SLS), have transformed the fabrication of TiO₂ architectures, allowing the fabrication of intricate complex structures with high precision and customization. These technologies facilitate the integration of TiO₂ into polymeric composite matrices, enabling the development of hierarchically structured materials with improved photocatalytic activity. Their controlled, layer-by-layer deposition empowers the creation of gradient and spatially varied compositions, resulting in multifunctional materials that combine superior photocatalytic performance with enhanced mechanical properties. Moreover, the inherent versatility of 3D printing reduces material waste, increases design flexibility, and accelerates both prototyping and implementation. Given these distinctive capabilities, 3D printing is increasingly regarded as a viable and versatile platform for fabricating advanced photocatalytic reactors.^4,5 In addition, it is also considered a viable approach for building integrable photocatalytic reactor designs.^9,10 As statistically demonstrated in Fig. 1(a), research towards 3D-printed TiO₂ structures started in 2014–2015 and has rapidly progressed over the past few years. Nearly two-thirds of the research published on 3D-printed TiO₂ focused on photocatalytic applications.

Fig. 1 Research statistical data from various studies of 3D-printed TiO₂ structures: (a) research articles published over the years, (b) photocatalytic applications, (c) photocatalytic degradations, and (d) other functional applications (filtered data in graphs is collected from the year 2014 to 2025 via Web of Science database using the keywords: TiO₂ and 3D-printing).

By precisely adjusting the geometry and material composition, these 3D printing approaches significantly enhance photocatalytic efficiency and broaden the potential utility of TiO₂ across other domains. Fig. 1(b)–(d) display pie charts summarizing statistical research trends on 3D-printed TiO₂ for various applications. 3D-printed TiO₂ architectures are primarily used for photocatalytic wastewater treatment, antimicrobial and self-cleaning surfaces, air purification, H₂ production, and other photocatalytic and non-photocatalytic functional applications (as shown in Fig. 2).¹¹ In this review, we comprehensively described how 3D-printed TiO₂ serves as a multifunctional platform (wastewater treatment, antimicrobial surfaces, hydrogen production, air purification, N₂ fixation, optical/photonic, construction, thermal-mechanical, and biomedical applications), whereas the only existing earlier review was limited to organic pollutant degradation.¹² In this review, we discussed the details on various 3D printing methods and their performance (photocatalytic and non-catalytic) comprehensively, with dedicated subsections for methods, mechanisms, each application area, and a forward-looking summary.

Fig. 2 Schematic demonstration of various applicable studies of 3D-printed TiO₂ structures and related primary printing methods.

2. 3D printing methods for TiO₂

3D printing is commonly used to fabricate membranes, monoliths, scaffolds, and filters for photocatalytic and other functional applications. 3D printing of TiO₂ encompasses various techniques, as per various studies, primarily grouped into four sections based on the printing mechanisms: DLP/SLA; DIW; FDM/FFF; and SLM/SLS, as shown in Fig. 3. Vat photopolymerization (DLP/SLA) relies on spatially resolved curing of a TiO₂-loaded photocurable resin in a liquid vat, using either a scanning laser (SLA) or projected digital light pattern (DLP) to solidify each layer. DLP/SLA method emerged as the leading choice for TiO₂ 3D printing, because it offers sub-tens-of-micrometer resolution, high dimensional accuracy, and the ability to realize complex, thin-walled lattice architectures with high surface-to-volume ratio, which are advantageous for photocatalytic reactors and other functional components. Additionally, it enables the simple fabrication of TiO₂-based thin films on substrates for various applications.¹³ Material extrusion covers both DIW and FDM/FFF, but the underlying working principles differ in the way the feedstock is delivered and solidified. DIW is an extrusion-based 3D printing method in which a viscous ink is pushed through a nozzle under pressure and deposited layer by layer to build the desired geometry. It is particularly suited to ceramic- or nanoparticle-rich inks, such as TiO₂ slurries, because their paste-like nature allows high solid loading while remaining printable. Shape retention is governed by ink rheology and rapid gelation or solvent loss after deposition, which makes DIW well-suited for open woodpile, honeycomb, and foam-like TiO₂ monoliths with hierarchical porosity. Unusually, Sopha et al. first DIW-printed the Ti woodpile and then anodized it to produce TiO₂ nanotubes on its surface.^14,15 FDM/FFF is a filament-based extrusion process in which a thermoplastic wire is heated, extruded through a nozzle, and deposited layer by layer. When TiO₂ is incorporated into the filament, this method enables low-cost, desktop fabrication of TiO₂-containing structures and scaffolds. FDM and FFF printing methods are also the same, except for their usage terminology (FDM is an industrial-grade method, while FFF is a desktop 3D printing method). Due to nozzle-based printing and low-layer resolution, both DIW and FDM/FFF are only used to fabricate monolithic woodpile scaffolds.¹⁶

Fig. 3 Schematic demonstration of pronounced TiO₂ 3D-printing routes (DLP/SLA, DIW, FDM/FFF, and SLM/SLS) and their standard fabrication processing steps and usual geometrical printed structures.

Direct SLM/SLS 3D printing of TiO₂ is not widely adopted due to the difficulty of producing complex structures (primarily flat films), the significant effort required for powder handling and nitrogen environment, the high cost, and the high-power consumption.^17–20 Powder-bed-based SLM/SLS process, where a laser locally sinters or partially melts a powder layer to build the structures. In most cases, first SLM/SLS generates complex 3D metal scaffolds that are subsequently coated via anodization to form conformal TiO₂ nanotube layers, thereby combining the geometric freedom of powder bed fusion with the surface activity of TiO₂.^21–25 During coating to form a uniform, homogeneous TiO₂ coating on 3D structures, various parameters, such as electrolyte selection, heat-treatment time, and temperature, are critical.²⁴ Lastly, other 3D-printing methods, such as inkjet printing (IJP) and liquid deposition modeling, are also used to 3D-print simple thin-film TiO₂ structures for photocatalytic and solar cell applications.^26–28

In addition, impregnating or dispersing secondary dopants (e.g., metals or oxides) within the structures enhances photocatalytic or other functional activity. In most 3D printing methods, a significant amount of organic content is added: photoresin, photo initiator, binder, and/or dispersant in the DLP/SLA methods for light-based curing; PLA/ABS and binder in the FDM/FFF method for wire extrusion; and an organic solvent and binder in the DIW and IJP method for inkjet syringe flowability. Post-processing of printed structures, including heat treatments such as debinding, calcination, and/or pyrolysis/sintering, is necessary to eliminate or volatize most of the organic content. Step-wise controlled heat treatment is necessary to eliminate as much organic content as possible, without shrinkage or damage to the printed structures.²⁹ By controlling the process parameters, such as time, temperature, and environmental conditions of heat treatments, one can eliminate polymer degradation without compromising ceramic cracking, mechanical instability, phase instability, or structural collapse.³⁰ The overall advantages and limitations of the individual 3D printing methods are described clearly in Table 1. Compared with other methods, DLP/SLA offers the best solutions for producing TiO₂ parts with precise dimensional accuracy and complex, intricate application-oriented structures.

Table 1 Advantages and limitations of various 3D-printed TiO₂ methods¹²

Method	Key advantages	Main limitations
DLP/SLA	• High-dimensional accuracy helps to produce complex, intricate structures	• Additional post-treatments (curing, thermal treatments)
	• High printing resolution (sub-tens-of-micrometer) and faster printing rate
	• Enable complex, thin-walled structures with a high surface-to-volume ratio
DIW	• Suited for high TiO2 loading	• Only suitable for limited monolithic scaffold-type structures
	• Easier printability and cost-effective	• Limited or poor lateral resolution and demanding rheological content
FFF/FDM	• Low-cost and widely accessible process	• Very low layer resolution and low TiO2 content
	• Produce robust, stable TiO2 structures	• Restricted to simple scaffold designs
	• Suitable for both lab-scale and industrial printing	• High polymer fraction
SLM/SLS	• Self-supporting metallic scaffold	• High capital cost and energy-intensive
	• Mechanically very strong	• High wastage of the raw material and complex powder handling

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3. Photocatalytic performance and mechanistic considerations

Several investigations have demonstrated that the 3D-printed TiO₂ structures produced vigorous photocatalytic activity for various applications. The complete demonstration of 3D-printed TiO₂ structures (from their benefits and mechanisms to various photocatalytic applications) is shown in Fig. 4. The capacity of 3D printing to design bespoke geometries enables the creation of effective photocatalytic reactors and devices. The design freedom provided by 3D printing allows adjustment of flow dynamics and enhancement of the active surface area, thereby increasing the overall effectiveness of the photocatalytic process. After printing, the presence of TiO₂ on the surface of the structures is a critical factor regarding efficient photocatalytic reactions. As shown in Fig. 5(a), the common aligned and shifted geometric woodpile-type 3D-printed structures enhanced light penetration by a factor of 4 over the bulk structure on a macroscopic scale, strongly reflecting the high photocatalytic performance of 3D TiO₂ structures.³¹

Fig. 4 Schematic illustration of the photocatalytic mechanism and possible reactive species generation, and additional benefits of 3D-printed TiO₂ across various photocatalytic applications.

Fig. 5 (a) Schematic demonstration of the various structures, light penetration mechanism, and light absorption enhancement with the number of layers in the 3D-printed structures.³¹ (b) 3D-printed TiO₂ structure and its volume compressed with increasing the heat treatment temperatures.³³

In most studies, photocatalytic TiO₂ exists in two primary phases: rutile and anatase. The compound Degussa P25-TiO₂ consists of approximately 75% anatase and 25% rutile and is known for its high photocatalytic efficiency, making it the best choice to use in 3D-printed structures. As described in the previous section, heat treatment is critical for 3D-printed structures, as it primarily debinds and volatilizes the polymer content without transforming the TiO₂. For example, the volume of the 3D-printed TiO₂ structure compressed as the heat-treatment temperature increases, and the structure becomes more porous at high annealing temperatures, as shown in Fig. 5(b). For P25 TiO₂, the optimum heat treatment (180 °C for 30 min, then 250 °C for 30 min, then 350 °C for 30 min) applied to the printed structures does not alter the active anatase/rutile ratio.³² In addition to post-treatment on the 3D-printing structures, the photocatalytic activity or other functionality is further enhanced by incorporating conductive elements, such as metals, graphene, oxides, or polyaniline, into TiO₂-printing structures. In photocatalysis, this boosts charge-carrier mobility and minimizes recombination rates by acting as co-catalysts or forming heterojunctions. The details of the 3D-printed structural designs, material optimizations, and related photocatalytic performances and other applications are explained in the following sections.

3.1 Wastewater treatment

The significant challenges in wastewater treatment or filtration systems are durable immobilization of catalyst materials, the high cost of catalytic filtration, and the potential for cross-contamination of treated water.³⁴ In addition, a large surface area and the hydrophilic nature of the catalyst material are required for the efficient photocatalytic degradation of pollutants; hence, balancing high surface area, hydrophilicity, durable immobilization, and cross-contamination is achieved by 3D printing of TiO₂. In addition, 3D-printed TiO₂ structures demonstrated strong reusability and recyclability in photocatalytic performance without compromising degradation efficiency.³⁵ A simple 3D-printed TiO₂-based lattice architecture enabled safe, strong, portable, self-supporting, efficient, and high-surface-area water disinfection without the need for expensive, complex catalytic filtration.³⁴ The complete schematic demonstration (from material mixture to 3D printing to installation and UV exposure) of water purification using 3D-printed TiO₂ is shown in Fig. 6(a). Zhou et al. prototyped and designed a 3D-printed sinusoidal TiO₂-based photocatalytic flow reactor for wastewater purification.³⁶ The comparison of the degradation performance of 3D-printed TiO₂ architectures with conventional powder and thin-film materials is shown in Fig. 6(b). From the figure, it is clear that 3D-printed TiO₂ structures significantly improve the photocatalytic degradation performance compared with conventional powders and bulky structures.

Fig. 6 (a) Schematic demonstration of the most-adopted 3D printing processing route towards wastewater treatment (from initial resin preparation to DLP 3D printing to post-processing to final photocatalytic activity of wastewater treatment). (b) Comparison of the methylene blue photocatalytic degradation performance of conventional TiO₂ powder and bulk cube with 3D-printed structure,³⁷ and (c) degradation efficiencies of various organic dyes with a 3D-printed TiO₂ structure. Reproduced with permission from American Chemical Society.³⁵ Copyright 2024.

Methylene blue (MB) is a well-studied organic dye for the photocatalytic degradation of organic pollutants using various 3D-printed TiO₂ structures. The degradation efficiency of various organic dyes reached over 90% using the optimal 3D-printed TiO₂ structure (Fig. 6(c)). As summarized in Table 2, the degradation rates and efficiencies varied significantly due to the adopted 3D printing method, the TiO₂ loading concentration in the structures, and the additional loading of additives and dopants. Various optimization methods have been adopted to enhance the photocatalytic degradation performance. For example, the novel hierarchical 3D hollow microarchitecture, composed of a TiO₂/Fe₂O₃ heterojunction, facilitates the degradation of MB and acetaminophen via a solar-driven photo-Fenton catalytic reaction.³³ In another study, anodized TiO₂ nanotubes on 3D Ti–1% Nb meshes exhibited the highest acetaldehyde photocatalytic activity, owing to a reduced bandgap resulting from Nb defects introduced into the nanotubular crystalline lattice and minimal electron–hole recombination.¹⁵ In another study, adding CNTs to a 3D structured compound parabolic reactor composed of TiO₂ improved photocatalysis and photolytic cleavage of amoxicillin pollutants.⁶⁹ Overall, incorporating secondary elements/compounds and optimizing structures with a high surface area and enhanced convective mass transport during 3D printing of TiO₂ results in enhanced photocatalytic wastewater treatment.

Table 2 Summary of photocatalytic degradation performance of various 3D printed TiO₂-based systems

Material	Method	3D-structure	Load (%)	Pollutant	Degradation efficiency (%)	Irradiation time (h)	Rate constant (h^−1)	Ref.
TiO2	DLP	Diamond	50	Methylene blue	99	10	0.76	35
TiO2	DLP	Octet	20	Methylene blue	93	6	—	37
TiO2	DLP	Gyroid	36	Carbamazepine	40	2	—	38
TiO2	DLP	Square grid	10	Rhodium B	85.8	6	0.28	39
TiO2/CdS	DLP	NPR	9	Rhodium B	100	1.25	—	40
TiO2/graphene	DLP	BCC	0.5	Methylene blue	82.9	5	0.34	41
TiO2/Fe2O3	DLP	Kelvin	2	Methylene blue	95	3	—	33
TiO2/Fe2O3	DLP	Kelvin	2	Acetaminophen	100	2	2.72	33
TiO2	SLA	FCC	2	Arsenite	99.7	24	0.78	42
TiO2	SLA	Cylindrical fan	1	Rhodium B	80	4	—	10
TiO2/SiO2	SLA	Hexagonal scaffold	5	Methylene blue	81.9	8	—	43
TiO2/SiO2/Sr	SLA	—	5	Methylene blue	84.5	8	—	44
TiO2	DIW	Woodpile	—	Tetracycline	94.3	3.5	—	45
TiO2	DIW	Woodpile	20	Methylene blue	100	1.25	—	46
TiO2	DIW	Honeycomb	66.5	Rhodium B	99	3.2	1.14	47
TiO2	DIW	Woodpile	63	Primidone	50	3	0.16	48
TiO2	DIW	Film	10	Ciprofloxacin	46	4	0.30	49
TiO2	DIW	Film	3	Methylene blue	84.6	2	0.40	50
TiO2	DIW	Woodpile	63	Triclosan	99.5	4	0.66	51
TiO2	DIW	Woodpile	4.1	Methylene blue	92	10	—	52
TiO2	DIW	SLDD	2.2	Acesulfame	79	1	—	53
TiO2	DIW	Hollow foam	—	Methylene blue	97	3.33	1.05	54
TiO2	DIW	Woodpile	1	Amoxicillin	99.4	3	0.94	55
TiO2/Pd	DIW	Woodpile	45	4-Nitrophenol	100	0.17	44.16	56
TiO2/Pd	DIW	Pillars	—	4-Nitrophenol	99	0.33	16.2	57
TiO2/Pd	DIW	Woodpile	20	4-Nitrophenol	100	0.25	—	58
TiO2	IJP	Film	—	Rose Bengal	92	5	0.51	28
TiO2	FDM	Film	40	Acetaminophen	74	0.66	1.68	59
TiO2	FDM	Disk	20	Fluoranthene	91	24	0.1	60
TiO2	FDM	Disk	20	Pyrene	94	24	0.12	60
TiO2	FDM	Gyroid	20	Microcystin	95.5	8	0.37	61
TiO2	FDM	F-RD	2.5	Methylene blue	93.4	2.5	—	62
TiO2	FDM	Gyroid	10	Methylene blue	81.5	12	—	63
TiO2	FDM	Square mesh	0.25	Methylene blue	13.5	2	—	64
TiO2	FDM	Woodpile	30	Methyl orange	100	24	0.04	65
TiO2	FDM	Dog-bone	10	Rhodium 6 G	22	4	—	66
TiO2/Ag	FDM	Square mesh	1	Acetaminophen	98	2	1.98	67
TiO2	FFF	Gyroid	37.5	Methyl orange	80	24	0.08	68
TiO2	FFF	Helix	1.5	Amoxicillin	5.3	2	0.03	69
TiO2	FFF	Diamond	34	Methylene blue	100	5	0.86	70
TiO2	FFF	Diamond	34	Microcystin	100	24	0.24	70
TiO2/AgCl/Ag	FFF	Gear	50	Methylene blue	99	1.7	2.25	71
TiO2/Cu	3D coating	Gyroid	—	Tetracycline	93.6	1	2.4	72
TiO2	3D coating	Woodpile	—	Methylene blue	91.8	0.8	3.0	14
TiO2	3D coating	Hologram	—	Methylene blue	91	0.5	3.54	73
TiO2	3D coating	BCC	5.4	Methylene blue	94.1	3	—	74
TiO2	3D coating	Monolith	—	Rhodium B	62	20	—	75
TiO2	3D coating	Octahedral	—	Methylene blue	92.5	3	—	76
TiO2	3D coating	Thin film	—	Benzothiazole	98	2	1.96	77
TiO2	3D coating	Thin film	—	Methylene blue	93	3.5	0.76	77
TiO2/Ag	3D coating	Cylinders	—	Rhodium B	94.5	3	—	78
TiO2/Ag	3D coating	Spiral	—	Rhodium B	30	5.83	0.07	79
TiO2/SiO2	3D coating	Rectangular mesh	—	Triton X-100	70	1.5	—	80
TiO2/ZnO	3D coating	Tetrapod	—	Tetracycline	90	2.5	0.92	81
TiO2/Cu/GO	3D coating	Gyroid	—	Methylene blue	93	2	—	82

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In addition to photocatalytic degradation of organic pollutants, 3D-printed TiO₂ structures are used in other wastewater treatment applications. For instance, a nanofiltration membrane made of DLP 3D printing with a TiO₂ and PEC-COOH active layer improves both hydrophilicity and permeation flux, while retaining 98.76% of the salt, demonstrating strong chlorine resistance and thus a high desalination capability for seawater.⁸³ Oil–water separation is crucial, particularly in offshore oil transportation, where frequent accidents harm the marine ecosystem and cause severe water pollution. In this regard, a 3D-printed composite membrane comprising an optimized ratio of TiO₂ and ABS efficiently rejects oil by promoting both hydrophilicity and oleophobicity.⁸⁴

3.2 Antimicrobial and self-cleaning surfaces

TiO₂ effectively damages or destroys microbes, primarily by generating reactive oxygen species (ROS), and induces DNA-cleaving oxidative reactions by damaging cellular membranes via UV irradiation. For example, FDM 3D-printed TiO₂ exhibits strong antibacterial performance, with 99.99% inhibition of S. aureus and 99.99% degradation of E. coli.⁸⁵ In another study, an SLS 3D-printed structure coated with TiO₂ exhibits anti-bacterial performance, achieving 90.11% and 90.60% degradation against S. aureus and E. coli, respectively.²⁵ As shown in Fig. 7(a), the 3D-printed TiO₂ pellets exhibited strong inhibition zones against S. aureus and E. coli, with inhibition zone diameters increasing with TiO₂ concentration.⁸⁶ In another antimicrobial study, S. aureus and P. aeruginosa are inhibited by TiO₂ agents incorporated into chitosan- or alginate-based macroporous 3D-printed hydrogels.^87,88 As shown in Fig. 7(b), the dispersion of Au nanoparticles on the 3D-printed Ti-structured TiO₂ anodized surface improved the antibacterial activity against S. aureus stained with acridine orange and ethidium bromide.²² For the practical demonstration, 3D-printed and surface-coated TiO₂ strongly degraded E. coli in the 3D-printed water processor tank.⁸⁹ In another practicality, the 3D-printed TiO₂ and mulberry anthocyanins-based bacteriostatic chromogenic structure inhibited S. aureus and E. coli, thus improving the quality (shelf life and freshness) of litchi fruit.⁹⁰ In addition, the viruses, such as Human Coronavirus 229E and Feline Calicivirus, are inhibited by 70% and 60%, respectively, after 4 hours of exposure to the 3D-printed TiO₂ structural surface.⁹¹

Fig. 7 (a) Antimicrobial susceptibility performance analysis on E. coli (red colonies) and S. aureus (yellow colonies) with increasing TiO₂ concentration (from left to right figures). Reproduced with permission from Springer Nature.⁸⁶ Copyright 2022. (b) Semi-quantitative graphs of antimicrobial activity of S. aureus on 1, 3, 5, and 7 days.²² (c) Enhancing the self-cleaning ability of cement with the addition of a small amount of TiO₂.⁹²

3D printing technology can produce the required rough surfaces by optimizing layer thickness and incorporating hydrophobic and photocatalytic fillers into printed parts, thereby enhancing the self-cleaning ability of the geometries. For instance, Zhan et al. 3D-printed and designed a self-cleaning surface by incorporating TiO₂ and SiO₂ fillers into a polyurethane matrix, demonstrating improved hydrophobicity and roughness, as well as enhanced MB degradation.¹⁷ As shown in Fig. 7(c), the addition of TiO₂ to the cement confers self-cleaning properties (color change upon exposure of the surface to RB dye) and improves the performance over time. Therefore, 3D-printed TiO₂ structures make systems and surfaces cleaner and safer.⁹²

3.3 Hydrogen production

TiO₂ is a well-established photocatalyst for water splitting and the reduction of methane or ethane to produce H₂ gas. Compared to traditional powder, the 3D-printed TiO₂ monolith demonstrated higher H₂ production due to enhanced interaction between incident light and the printed catalyst, resulting from its higher surface area, hierarchical micro- and nano-pores, and optimized size/shape.^93,94 For instance, as shown in Fig. 8(a), the design-optimized and hierarchically 3D-printed TiO₂ nanoporous aerogel with FCC lattice scaffolding demonstrated efficient light permeation and light harvesting, resulting in a hydrogen production rate almost five times higher than that of TiO₂ powder, which is further enhanced by dispersing Au nanoparticles.⁹⁵ Various design and engineering strategies are explored and adopted to improve the H₂ evolution rate with a 3D-TiO₂ structure. For instance, Schreck et al. designed a 3D polymer scaffold via DLP printing and then incorporated TiO₂/Pd aerogels into it.⁹⁶ In a comparative study, as shown in Fig. 8(b), with 3D-printed structural design optimization, he successfully demonstrated a 200% increase in hydrogen production rate, facilitated by greater UV light penetration and an enhanced reactive gas flow rate in the optimized structure.

Fig. 8 (a) H₂ production rate of 3D-printed TiO₂ compared to conventional powder TiO₂.⁹⁵ (b) H₂ production rate enhancement with structural modifications on the 3D-printed structure.⁹⁶ (c) Strong recyclability of H₂ production with a TiO₂ 3D-printed structure.⁹³ (d) Stable production of H₂ over long time in a designed 3D-printed TiO₂ microreactor.⁹⁷ (e) Comparison of the overpotential of 3D-printed TiO₂ structures (low overpotential indicates high H₂ production) with other reported H₂ production catalysts.⁹⁸

The engineering strategy of pre- and post-impregnating Au nanoparticles into the TiO₂ 3D-printed monoliths resulted in improved H₂ production from the water–ethanol mixture, especially in post-impregnation and calcination-treated monoliths.⁹⁹ In another case, TiO₂ is combined with a metal–organic framework, and the printed structure is then coated with Pt/PtO_x species, providing additional co-catalytic active sites and significantly enhancing the photocatalytic H₂ evolution reaction.⁹³ Furthermore, the designed and 3D-printed metal-based conical arrays of photoelectrodes are then anodized to form TiO₂ nanotubes, resulting in a significant enhancement in hydrogen production via photoelectrochemical water splitting.²¹ Next, the recyclability and reusability of the 3D-printed TiO₂ for H₂ production are robust, as evidenced by a 0.5% reduction in H₂ production rate after 5 cycles (Fig. 8(c)).⁹³ In addition, PLA 3D-printed TiO₂/Au-coated microreactor demonstrated a strong long-term photocatalytic ability for two days (Fig. 8(d)), revealing a stable hydrogen photoproduction rate in a water–ethanol gas mixture.⁹⁷ Furthermore, the designed micro- and macroscopically porous 3D-printed structure, consisting of TiO₂ nanotube arrays and Pt nanoparticles, demonstrates excellent H₂ evolution reaction performance and long-term stability due to its unique porous architecture, high active surface area, strong electronic metal–support interactions, and efficient carrier transport.⁹⁸ Overall, as shown in Fig. 8(e), overpotential (η) comparison of various reported hydrogen evolution reaction electrocatalysts, the 3D-printed structure consisting of TiO₂ outperforms (should be low η for high H₂ production) the most advanced platinum-based catalysts.

3.4 Air purification

TiO₂ is also known for reducing CO₂ and other toxic gases, such as NO, NO₂, O₃, LPG, and CH₃CHO, through its photocatalytic ability. For CO₂ reduction, Chen et al. fabricated an artificial leaf structure with TiO₂ by direct ink writing, which artificial photosynthesis via photo-reduction (enhances CO and CH₄ evolution).¹⁰⁰ In another instance, the heterojunction of TiO₂ with MoSe₂, with an optimal infill percentage in the 3D-printed structure, resulted in a CO₂ selectivity of approximately 82% through enhanced visible-light absorption, delayed recombination of electron–hole pairs, and promoted charge transfer of photogenerated electrons.¹⁰¹ Next, designed and fabricated a 3D-printed sinusoidal air-purifying photocatalytic reactor, made of a PLA and TiO₂ composite, which effectively removed 99% of O₃ and partially removed NO, NO₂, and CH₃CHO pollutants from the air.¹⁰² Next, to examine the effect of TiO₂ morphology on the removal of NO_x (both NO and NO₂) as gaseous pollutants, the 3D-printed UV100-TiO₂ showed higher degradation efficiency than P25-TiO₂, although its selectivity was poorer.¹⁰³

3.5 Other photocatalytic applications

Various other catalytic applications, such as N₂ photo-fixation, photoelectrochemical sensing, and photoanodes for batteries, are studied using 3D-printed TiO₂ structures. The designed macro- and micro-hierarchical, 3D-printed TiO₂ scaffold exhibits excellent potential for high surface adsorption and activation capacity, thereby promoting N₂ photo-fixation (the conversion of nitrogen to ammonia or other beneficial compounds).¹¹ In another instance, as shown in Fig. 9(a), novel designed 3D-printed hierarchical plasmonic heterostructure composed of vertical TiO₂ pillar arrays (as tree trunks), dense nanorod arrays (as branches), and plasmonic Au nanoparticles (as leaves) demonstrated a 15-fold high N₂ photo-fixation activity than its film due to the structure driven high active photocatalytic sites, multi-scattering of light, and enhanced plasmonic light absorption.¹⁰⁴ The 3D-printed TiO₂ hierarchical nanowire arrays with nanocavities have a greater surface area, more active sites, and shorter diffusion lengths for molecules during surface adsorption and reaction, thereby reducing response times and increasing sensitivity, resulting in an excellent photoelectrochemical sensor that surpasses a commercial P25-TiO₂ sensor.¹⁰⁵ In another study, a 3D-printed TiO₂/graphene/PANI-based molecularly imprinted micro-lattice-shaped photoelectrochemical sensor was developed, featuring a structure with designed, porous, interconnected macro-channels that enable the rapid spreading of incident light into the sensor interior, yielding high light absorption and highly efficient analyte diffusion/trapping throughout the entire sensor. The fabricated sensor demonstrated impressive ultrasensitive urea monitoring, with rapid response, low detection limit, wide linear range, exceptional selectivity, and stable operation.¹⁰⁶ A 3D-printed photocathode made of an oxygen vacancy-rich, hierarchically porous rutile TiO₂/rGO/CNT structure delivers a high discharge current density with a stable, long-life cycle, attributed to efficient photocatalytic sites and fast electronic/ionic pathways for efficient battery applications.¹⁰⁷

Fig. 9 (a) Schematic demonstration of the 3D-printing of forest-inspired hierarchical TiO₂/Au superstructure and related high light interaction-trapping mechanism and improved N₂ photo-fixation performance in 3D structure compared to a simple thin-film. Reproduced with permission from Wiley.¹⁰⁴ Copyright 2021. (b) Schematic of a dielectric photonic crystal, preceramic and calcinated 3D-printed TiO₂ woodpile architecture, and representative SEM images. Reproduced with permission from American Chemical Society.¹⁰⁸ Copyright 2020. (c) Optical profiling enhancement in the 3D-printed device by the incorporation of TiO₂.¹¹⁰ (d) TiO₂ incorporated 3D-printed rat anatomical phantom and its improved PL imaging after light absorption.¹¹¹ (e) Various properties enhanced by the addition of nano TiO₂ in the 3D-printing cement. Reproduced with permission from Elsevier.⁹² Copyright 2022. (f) Enhancement of printability (number of layers of 3D printing) of cement by increasing the TiO₂ concentration.¹¹⁸

4. Other functional applications

Besides catalytic applications, 3D-printed TiO₂ structures are being explored in other functional areas, including optical, photonic, electrical, construction, thermal, mechanical, and biomedical applications. As shown in Fig. 9(b), a sub-micron-level woodpile-type 3D-printed TiO₂ mesh is produced for optical-phonic sensors with high refractive index and transparency.^108,109 As shown in Fig. 9(c), TiO₂ surface treatment on 3D-printed objects improved the measurement of transparent surfaces using optical profilometry. Thus, the custom TiO₂ treatments offered better cost-effectiveness, potentially less waste, and customizability than commercial treatments, such as aerosol and microemulsions.¹¹⁰ The anatase TiO₂ in the 3D-printed structures demonstrated persistent photoluminescent properties due to slow electron migration, which is helpful for next-generation phantom PL imaging, as shown in Fig. 9(d).¹¹¹ The 3D-printed optical Ganzfeld bowl, coated with TiO₂ and serving as an integrating-sphere prototype, reflected all wavelengths equally and exhibited a radiance uniformity of 90%, comparable to the most expensive specialist coating, BaSO₄.¹¹² Vyatskikh et al. constructed and demonstrated 3D-printed TiO₂ with dielectric photonic crystal properties.¹⁰⁸ A 3D-printed TiO₂ thin film, serving as an electrode for a dye-sensitized solar cell, achieved a low sheet resistance of 6.8 × 10⁶ Ω square⁻¹ at a thickness of 6.25 µm, yielding an energy conversion efficiency of approximately 4%.²⁶ The simulated 3D-printed gyroid electrodes exhibit a greater concentration of Li⁺ ions within the printed structure than in the bulk, and experimental results also confirm that the 3D-printed TiO₂ electrode delivers higher discharge capacities than sodium-ion and lithium-ion batteries.¹¹³ The TiO₂ 3D-printed monolithic ceramic filter exhibits excellent dielectric properties and effective filtering at microwave frequencies.^114,115 In addition, the 3D-printed TiO₂ resin exhibited strong gamma-ray attenuation with a low TiO₂ rate, demonstrating strong electromagnetic shielding properties.¹¹⁶ A 3D-printed film combining a litmus indicator with TiO₂ functionality served as a pH sensor, and the fabricated sensor demonstrated excellent stability and reversibility.¹¹⁷ Other well-studied non-catalytic functionalities of 3D-printed TiO₂ structures have been discussed in the following sections.

4.1 Construction applications

Incorporating TiO₂ into 3D-printed construction or building materials can give long-term photocatalytic capabilities, resulting in self-cleaning surfaces and air filtration with lower maintenance costs. In addition, TiO₂ played a crucial role in enhancing the quality, stability, and service life of cement in 3D-printed cementitious structures.⁹² In the construction sector, the overall benefits of incorporating TiO₂ into 3D-printed cement materials are presented in Fig. 9(e). Moreover, in the TiO₂-dispersed cementitious composite, the added TiO₂ content helped reduce build time and significantly increased the number of printing layers compared to pristine cementitious materials, as shown in Fig. 9(f).¹¹⁸ TiO₂ also improves hydration, density, compression strength, and thickening properties, thereby reducing slumping and flow diameter in 3D-printed cement, making it non-porous, stronger, and easier to build.⁹² In addition, incorporating TiO₂ particles provided beneficial filling and nucleation effects in the cement-based material, specifically filling the voids within the 3D-printed specimens and increasing their density.¹¹⁹ Moreover, the TiO₂ particles facilitated hydration by providing additional nucleation sites, thereby enhancing the compressive strength of the specimens under identical environmental conditions. The coating of TiO₂ onto the 3D-printed cement structure effectively degrades rhodamine B, opening the door to photocatalytic coatings in the construction industry for air filtration and self-cleaning.⁷⁵

4.2 Thermal and mechanical applications

TiO₂ incorporated into a 3D-printed structural polymer enhances crystallinity, thermal stability (decomposition and glass transition temperatures), fluidity, and filament flowability, and manipulates surface texture (rough or smooth, depending on the matrix).^120–122 Further, the glass transition temperature of the 3D-printed polymers increased with increasing TiO₂ concentration.¹²³ The addition of TiO₂ to the 3D-printed Al₂O₃ led to increased ceramic grain growth and the formation of secondary Al₂TiO₅, thereby enhancing the bulk density, sintering kinetics, residual flexural strength, and thermal shock resistance.¹²⁴ Similarly, the addition of optimal MgO to the 3D-printed TiO₂ resulted in the growth of ceramic grains and the formation of secondary MgTi₂O₅, thereby enhancing the bulk density and bending strength and reducing the sintering temperature.¹²⁵ The mechanical stability and erosion resistance are also improved in the 3D-printed TiO₂ structures.³² The tensile strength and elongation significantly improved with the addition of TiO₂ to the 3D-printed PLA structures.¹²² As shown in Fig. 10(a), various mechanical properties, including tensile strength, modulus of elasticity, flexural strength, toughness, and microhardness, of the 3D-printed polymer structures improved upon incorporating TiO₂.^126,127 The addition of Zn to 3D-printed TiO₂ facilitated the formation of foam-like structures, yielding compression strengths and elastic moduli comparable to those of ceramic foams produced by conventional manufacturing techniques.¹²⁸ Overall, TiO₂-based 3D-printed composite structures enhance thermal and mechanical stability, making them suitable for load-bearing structural applications.

Fig. 10 (a) Various mechanical properties improved strongly by the incorporation of TiO₂.¹²⁶ (b) Live–dead and cytoskeleton-stained fluorescence images of cell proliferation on the TiO₂ 3D-printed scaffolds with different pore sizes over time. Reproduced with permission from Elsevier.¹²⁹ Copyright 2024.

4.3 Biomedical applications

TiO₂ is also known as a bio-ceramic oxide with exceptional bioactivity and biocompatibility; hence, its 3D-printed structures are also being studied in the context of orthopedic scaffolds and dental fixations, where 3D printing methods enable the fulfillment of design complexity, arbitrary shaping, fast production, and dimensional accuracy. The 3D-printed TiO₂ composite structures demonstrated improved bioactivity, enhanced cell proliferation and extracellular matrix mineralization, and facilitated osteogenic differentiation, offering optimal mechanical properties that support biomedical applications such as bone fixation and regenerative bone scaffolds.^22,130 As demonstrated in Fig. 10(b), the macro- and micro-porous 3D printed TiO₂ scaffold, which exhibits strong proliferation and osteogenic differentiation properties, further improves over time in rabbit bone marrow mesenchymal stem cells.¹²⁹ In comparison to 3D-Ti and TiO₂ scaffolds, the Ag-dispersed 3D-TiO₂ bone scaffolds showed significant amounts of uniformly distributed neo-plastic bone tissue in their pores, as well as genes and proteins associated with osteocalcin, collagen type I, and alkaline phosphatase that were more elevated and biocompatible with the surrounding tissues.²² In addition, 3D-printed calcium silicate scaffold enriched with TiO₂ retains optimal porosity and demonstrates enhanced compressive strength, a slower degradation rate, and significantly increased osteogenic induction and angiogenic activity in bone regeneration. Furthermore, experiments using a cranial bone defect model have demonstrated that the 3D-printed calcium silicate/TiO₂ scaffold can significantly accelerate vascular neogenesis and bone regeneration, fully confirming its broad application potential in bone defect treatment.¹³¹ The PLGA–TiO₂ composite scaffolds fabricated via 3D printing exhibited favorable mechanical and biological properties, supporting cell viability, osteoblast culture, enhanced calcium secretion, and increased ALP activity, all of which are essential for bone tissue regeneration.¹³²

Both dental and bone-related structures require high mechanical strength, which is enhanced by increasing the TiO₂ concentration in the 3D-printed bio-parts.⁸⁸ Compositing PLA with TiO₂ significantly enhanced the mechanical, wear, and frictional properties of 3D-printed bio-components, which are highly desirable in regenerative bone-joint applications.¹³³ Other studies have revealed that 3D-printed TiO₂ composites exhibit good in vitro bioactivity and biocompatibility, including cell proliferation, viability, and adhesion, making them attractive candidates for biomedical applications in bone replacement treatments due to their cancellous bone-like characteristics and potential use in dental fixtures.^88,134,135 The exceptional mechanical strength, good antibacterial activity, and low cytotoxicity of the 3D-printed reinforced composite of PMMA/TiO₂/PEEK demonstrate tremendous promise as a material for realistic dental restorations.¹³⁶ Inspired by the organic-inorganic enamel biostructures of teeth, Wei et al. synthesized a TiO₂ columnar nanorod framework using microscale additive manufacturing.¹³⁷ The resultant design resembles an enamel-like structure, with comparable hardness, an ultra-high Young's modulus, and superior viscoelastic properties. The integration of TiO₂ nanoparticles into 3D-printed denture base resin significantly enhanced properties, including flexural strength/modulus, impact strength, Vickers hardness, DC, and solubility, compared to the unmodified material; however, the influence on saliva sorption and Martens hardness was negligible.¹³⁸ The addition of TiO₂ nanoparticles to 3D-printed dental resin restorations has strong potential to improve the longevity of long-term interim implant-supported restorations.¹³⁹ Furthermore, TiO₂-containing 3D-printed nanocomposite denture base resins exhibited increased surface roughness and color change without altering hardness; this impact was resin-dependent. Therefore, selecting an appropriate resin material for nanocomposite fabrication should be considered.¹⁴⁰

Conclusively, the overall advantages of TiO₂ 3D printing over traditional methods, including performance, are demonstrated in Table 3. As summarized in the table, 3D-printed TiO₂ consistently outperforms powder dispersion and films across several key metrics, including light penetration, pollutant degradation kinetics, hydrogen productivity, structural integrity, and recovery and reusability.

Table 3 Advantages of 3D-printing over conventional power and film-based TiO₂

Performance metrics	Conventional TiO2	Advantages of 3D-printed TiO2	Evidence source
Light penetration efficiency	Minimal penetration in powders due to aggregation and dispersion issues^141	Strong light-penetration enhancement. Customizable reactor geometry design	Fig. 5(a) demonstrates geometric enhancement through aligned and shifted woodpile architectures versus bulk materials
Photocatalytic degradation rate	Moderate rate with powder accumulations, gravity settling, and low-surface area exposure	Rapid kinetics expressed with multiple design optimizations	Table 1: DIW/woodpile structures degrade methylene blue (100% in 1.25 h) and triclosan (99.5% in 4 h) versus powder benchmarks requiring extended timeframes
Hydrogen generation capacity	Significantly lower volumetric H2 output; rapid deactivation^95	Higher production than TiO2 powder; sustained performance over multiple cycles	Fig. 8(a): FCC lattice-structured aerogel demonstrates near-stoichiometric improvement; 3D architecture enables efficient light harvesting and gas-phase transport
Structural integrity, recovery, and recyclability	Either wash-out or cross-contamination from leaching particles^142	Eliminates contamination risk; reusable across applications; self-supporting lattice structures with immobilization; zero nanoparticle leaching after multiple cycles	Conventional dip-coating and spraying methods produce non-uniform films prone to delamination, whereas 3D-printed monoliths achieve recovery without loss of catalytic activity
Mechanical & thermal robustness	Limited mechanical contribution in conventionally processed TiO2	Dual functionality: photocatalytic + load-bearing capacity; enhanced tensile strength, modulus, and flexural resilience; improved glass transition temperature with loading	Incorporation into 3D polymer matrices elevates tensile strength by measurable margins and enables thermal stability up to controlled glass-transition temperatures, expanding applications in structural components

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5. Summary and future prospects

The integration of 3D printing technology with TiO₂ represents a significant breakthrough in photocatalysis and various multifunctional applications. This technology offers several unique advantages, including the ability to fabricate complex and precise geometries with tunable and integrated material properties, along with easy recyclability and reusability, making it a promising option for environmental remediation and ecological applications. This review provides a comprehensive overview of TiO₂ 3D printing research and fabrication methods, while highlighting its potential for future innovations in the rapidly expanding fields of environmental remediation and other advanced functional applications. The literature available on 3D-printed TiO₂ architectures projects its suitability for clear real-world promise in the photocatalytic applications for a wide range of applications that include wastewater treatment, air purification, antimicrobial and self-cleaning surfaces, and hydrogen production. These applications are feasible mainly because in 3D printing, the catalyst can be immobilized within robust lattices and enable engineered flow and light management under practical operating conditions. 3D-printed TiO₂ architectures also show promise for other catalytic and non-catalytic applications, such as N₂ fixation, construction, thermal, mechanical, biomedical, and others. The 3D-printed TiO₂ architectures provide mechanical and thermal functionalities, such as improved tensile strength, flexural resilience, and higher glass-transition temperatures, and help in preserving a dual role: as a photocatalytic active surface and a stabilized structural component.

Regarding advancements in photocatalysis, future research should focus on the development of novel composite photocatalytic materials based on TiO₂ and the optimization of relevant 3D printing procedures to enhance the performance, stability, and durability, leading toward practical and large-scale applications. Furthermore, fabricating hybrid photocatalytic composite systems based on 3D-printed TiO₂, is expected to enhance photocatalytic efficiency. Research in this direction is demanding. Economically, these systems benefit from low-cost feedstocks and scalable additive manufacturing techniques such as DLP, DIW, and FDM. However, they still encounter significant challenges related to the cost of photopolymer resins, post-processing heat treatments, and relatively slow printing speeds, which currently limit their implementation to pilot-scale rather than fully commercial deployment. Long-term durability is considerably superior for 3D printing technology than that of powder- and film-based systems, as 3D-printed structures exhibit strong resistance to delamination, retain photocatalytic activity over repeated cycles, and effectively minimize nanoparticle leaching. It is envisioned that future studies should highlight, addressing the fouling and stability gaps via smarter geometries, doped composites, and surface modifications is essential to translating 3D-printed TiO₂ into reliable infrastructure technologies. Despite promising progress in 3D-printed TiO₂ structures, substantial future research is still required to address practicality parameters, such as scalability, techno-economic feasibility, long-term durability, operational stability, and commercialization prospects.

Author contributions

V. C. S. Theja and V. Karthikeyan: writing – original draft; Y. Guo and C. S. Yeung: literature review and data curation; S. Choudhary, V. Kannan, and D. S. Assi: writing review & editing; G. Saianand and G. A. Iyengar: conceptualization, editing, and funding; D.-E. Lee: funding acquisition; V. A. L. Roy: supervision, project administration, funding acquisition.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data sharing is not applicable to this article as no new data were generated or analyzed in this study.

Acknowledgements

This research was funded by the following grants: the Research Grants Council of the Hong Kong Special Administrative Region under the Institutional Development Scheme – Collaborative Research Grant Project (UGC/IDS(C)16/P01/24) and National Research Foundation of Korea grant funded by the Korean government (SMIT) (NRF-2022R1A2C1092289 and NRF-2018R1A5A1025137).

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Footnote

† Vaskuri C. S. Theja and Vaithinathan Karthikeyan contributed equally to this work.

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