Cubic Ag/AgBr–graphene oxide nanocomposite: sono-synthesis and use as a solar photocatalyst for the degradation of DCF as a pharmaceutical pollutant

Abstract

In this study, novel Ag/AgBr/graphene oxide (GO) nanosheets were successfully prepared via a facile and fast sonochemical route for the first time, and ultrasound has a key role in the preparation process. Ag nanoparticles were formed on the surface of cubic AgBr in the composite by photo-reduction through sunlight irradiation. The physical and photophysical properties of the as-prepared Ag/AgBr/GO nanocomposite were characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflection spectroscopy (DRS) and Raman spectroscopy techniques. Moreover, the Ag/AgBr/GO nanocomposite exhibited excellent photocatalytic activity under sunlight illumination to decompose diclofenac sodium (DCF), which is an important pharmaceutical pollutant. The decomposition of DCF by the sonosynthesized sample was done within 6 min, which may be attributed to its large surface area as well as superior charge separation and transfer efficiency. Furthermore, the COD and stability of the catalyst were investigated.

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1. Introduction

Semiconductor materials play an essential role in several areas of our life, such as energy harvesting, conversion and environmental applications, which include photocatalysis, photoelectrolysis, and photovoltaics.^1–6 To date, the development of highly efficient photocatalyst nanostructures for the elimination of pollutants from air and water has been considered to be one of the important investigative fields.^7–10 However, photocatalysts with solar light absorption are still an impasse for practical applications. Plasmonic noble metals (typically gold and silver) have played an important role in the field of photo driven chemical conversion due to their surface plasmon resonance (SPR).^11,12 AgBr, which is a high-quality photosensitive material for photography, has recently attracted researchers' attention because of its excellent visible-light-response photocatalytic performance. For applications, AgBr is usually loaded on other materials to enhance its catalytic properties.^13–15 By employing SPR on noble metal nanoparticles, some highly efficient visible light response plasmonic photocatalysts have been developed.^16–22 Photocatalysts, such as the AgBr/Y-zeolite composite, are too unstable for practical application.²³ As a result, the stability of these catalysts is also an important factor that must be considered. Ag/AgBr catalyst shows high photocatalytic activity and stability under visible light irradiation.

It is known that well-controlled hierarchical structures, particularly 3D structures, could provide high specific surface areas with well aligned pore structures, which shorten the diffusion paths to active surface sites.^1,24 For example, the hierarchical structures of green leaves in certain photosynthetic plants are optimized for efficient light harvesting and sunlight conversion to chemical energy by the photosynthesis process.²⁵ For photocatalytic or photovoltaic applications, similar structures can be used as a means of improving photoenergy conversion efficiency due to the enhanced light harvesting, short charge-carrier transport paths, and increased active sites in porous micro or nano channels.^26,27 However, the synthesis of AgBr nanostructures with special morphologies has been seldom reported. To adjust the quality and morphology of plasmonic photocatalysts in nanostructures and composites, various amphiphilic molecules and surfactant have been used.¹¹ Recently, shape-directing surfactants or specific surface capping agents, such as polyvinyl pyrrolidone (PVP) and cetyltriethylammonium bromide (CTAB), were applied to guide the formation or induce anisotropic growth of different Ag/AgBr composites. However, the presence of large amounts of these agents leads to a decrease of active sites, which severely affects the photocatalytic activity of these photocatalysts.^28,29 Therefore, it is an important challenge to develop morphology-controlled photocatalysts with a “clean” surface structure. The emergence of single-layer graphene oxide (GO) has received extensive attention and showed great potential as an ideal additive for controlling the formation of inorganic single crystals. This is due to its unique two-dimensional (2D) nanostructure, good flexibility and many functional groups, such as hydroxyl, epoxy and carboxyl, on its surface.³⁰ On the other hand, graphene oxide has been proven to be a competent coupling material to enhance the quantum yield of semiconductor photocatalysts and help to disperse and stabilize inorganic nanoparticles. The oxygenated functional groups of GO could act as active sites for the heterogeneous nucleation of metal ions. In addition, the large surface area and tuneable surface properties of GO allow it to be a good host substrate for the heterogeneous growth of demanding guest particles. Furthermore, the growth of nucleated clusters on the GO surface may yield final particles with suitable sizes and microstructures.¹¹

In the present study, using the advantages of Ag/AgBr and GO, a nanocomposite of Ag/AgBr/GO was synthesized by ultrasound with a controlled cubic morphology of AgBr for the first time.

Ultrasound irradiation has various effects on chemical processes, which include wide ranging applications in composite synthesis, catalytic reactions, and environmental sciences.^31–35 The acoustic cavitation produces bubbles, which grow and then implosively collapse, thus creating localized hot spots during the rarefaction phase of sound waves with cooling rates above 1 × 10¹⁰ K s⁻¹ and pressures of the order of 100 MPa.³⁵ The kinetic energy released under these extreme conditions promotes both physical effects and chemical reactions, which can directly influence the particle size and morphology of the synthesized products.

Herein, for the first time, a facile sonochemical approach was developed for the synthesis of a 3D structure and physically stable Ag/AgBr/GO nanocomposite. The obtained Ag/AgBr/GO shows a cubic structure of AgBr and Ag nanoparticles are formed on the GO surface very well. Furthermore, the photocatalytic performance of the as-prepared photocatalyst was carefully investigated for the removal of DCF from the aqueous solution.

2. Experimental section

Materials

Graphite powder (purity 99%, mesh 325), potassium permanganate (KMnO₄), sodium nitrate (NaNO₃), sulfuric acid (H₂SO₄), hydrochloric acid (HCl), hydrogen peroxide (H₂O₂), silver nitrate (AgNO₃, 99%), potassium bromide (KBr), and polyvinylpyrrolidone (PVP, K29-32, average M_w = 58 000) were obtained from Merck. Absolute ethyl alcohol (EtOH) was obtained from Hamoon teb markazi, Iran. DCF was obtained from Sigma Aldrich. All materials were used as received without additional purification or treatment. De-ionized water (DI) was used in the synthesis of GO.

Synthesis of GO

GO was prepared by ultrasound based on our recent study.³⁶ In a typical procedure, 0.5 g graphite and 0.5 g NaNO₃ were added to 23 mL H₂SO₄. The mixture was stirred in an ice bath and then, 3.0 g KMnO₄ was gradually added. After that, the suspension was placed in an ultrasonic bath and irradiated for 20 min at room temperature. The prepared suspension was diluted by 40 mL DI water. Finally, 100 mL DI water with 3 mL H₂O₂ (30%) was added to the suspension. The mixture was filtered and washed with aqueous HCl solution and distilled water and dried under vacuum at 80 °C for 24 h. To obtain GO nanosheets dispersed in EtOH, 100 mg of as-synthesized dried solid product was added to 100 mL of ethanol. Then, the suspension was treated with an ultrasonic homogenizer (Branson Digital Sonifier, W-450 D, frequency = 20 kHz) for 1 h.

Synthesis of nanocomposite as a photocatalyst

The Ag/AgBr/GO nanocomposite was synthesized using an ultrasonic route. In a typical procedure, AgNO₃ ethanol solution was prepared by dissolving 169 mg (1 mmol) AgNO₃ and 1200 mg polyvinylpyrrolidone K29-32 (PVP) in 20 mL absolute ethyl alcohol. A KBr saturated aqueous solution was also prepared in advance. Then, 4 mL saturated KBr aqueous solution was injected into 100 mL GO ethanol mixture. Subsequently, 20 mL of the AgNO₃ ethanol solution was poured into the KBr/GO ethanol dispersion. The mixture was sonicated for 3 h at a temperature below 10 °C, and AgBr on the GO surface was obtained. Ag nanoparticles (NPs) were generated on the surface of AgBr using the method of photoreduction (PR). The AgBr/GO ethanol dispersion was illuminated using solar light for 30 min to form Ag/AgBr nanoparticles on the GO nanosheets. Finally, the collected Ag/AgBr/GO sample (Ag/AgBr/GO (U)) was washed with water and absolute ethyl alcohol to remove KBr and other impurities. For comparison, Ag/AgBr with a cubic morphology was synthesized via a parallel procedure without GO. In addition, the Ag/AgBr/GO particles were synthesized using conventional method without the well-defined morphology of AgBr³⁷ (Ag/AgBr/GO (C)).

Sample characterization

The crystal structure of the sample was investigated using X-ray diffraction (XRD; Bruker-AXS D8 Advance model at a scanning rate of 0.04° s⁻¹, with monochromatized Cu Kα radiation (λ = 1.5406 Å)). Fourier-transform infrared spectroscopy (FT-IR) was conducted on a Thermo Nicolet 370 spectrometer and the spectrum was obtained by mixing the sample with KBr. Raman spectroscopy was performed using an Almega Thermo Nicolet Dispersive Raman Spectrometer with 532 nm laser excitation. The morphology of the samples was examined using a scanning electronic microscope (SEM, LEO 1450VP). The optical properties of the catalyst were investigated using UV-vis diffuse reflection spectroscopy (DRS) on a MC-2530 spectrophotometer using BaSO₄ as the reference material. Photocatalytic activity was studied by determining the concentration of DCF in solution via UV-vis spectroscopy (Unico 2800). Ultrasonic irradiation was applied with an equipment operating at 20 kHz (Branson Digital Sonifier, W-450 D) and a bath ultrasound (Branson, model 8510E-DTH, USA, 40 kHz, 250 W).

Photocatalytic activity

The photocatalytic activities of the as-prepared samples were evaluated by the degradation of DCF in an aqueous solution under sunlight irradiation. In this study, the Minitab software was used to design science statistical experiments to consider all contingencies and the optimized parameters for the best response. Table 1 in the supplementary information shows the experimental design for DCF degradation through 9 experiments, 3 variables, 3 levels for each variable based on the factorial Taguchi design.

Table 1 Comparison of different parameters of the present system with other relevant systems on DCF degradation

Parameter	Our work	Ref. 49	Ref. 50	Ref. 51	Ref. 52
Catalyst	Ag/AgBr/GO	TiO2	MWCNT (multi-walled carbon nanotube)	TiO2 + SiO2 + Fe3O4	TiO2
Light source	Sun light	UV light	NUV-vis, UV light	UV light	UV light
Degradation time (min)	6	200	NUV-vis: 40 UV: 16	45	140
Easiness	Does not need H2O2 or UV light or any special thing	Special setup due to membrane	Needs H2O2 + O2	Special set up due to electrode	H2O2, pH = 4, special reactor
Efficiency of degradation	93%	99.5%	—	95.3%	80%
Material and method	Nano composite photocatalyst	Photo-catalytic membrane reactor	Heterogenous catalyst	Photoelectrocatalytic	Hydrodynamic cavitation reactor
DCF concentration	25 ppm	2.5 ppm	8 ppm	1 × 10^−3 mol L^−1	20 ppm

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For comparison, the same photocatalytic degradation experiments were performed with Ag/AgBr/GO (U) and Ag/AgBr. In a typical experiment, 0.03 g photocatalyst powder was suspended in 25 mL DCF aqueous solution (25 mg L⁻¹) at its natural pH. The solution was stirred vigorously in the dark for 30 min to establish adsorption–desorption equilibrium. After that, direct solar radiation on consecutive sunny days between 10 am and 2 pm (GPS coordinates: N = 36° 18′41.6′′, E = 59° 31′ 54.2′′) was used as the visible light source to irradiate the suspension under vigorous stirring. Samples were collected from the reaction mixture at different time intervals and then centrifuged twice at 7000 rpm for 5 min to separate the solid photocatalyst particles completely. The top transparent solutions obtained were then transferred to a quartz cuvette to measure their absorption spectra in the wavelength range of 200–400 nm. The degradation percentage is reported as C/C₀, where C₀ is the initial concentration of DCF and C represents the corresponding concentration at a certain time interval. The relative concentrations (C/C₀) of the DCF solutions were determined by their relative absorbance (A/A₀) at 275 nm. In addition, the photocatalytic activity of Ag/AgBr was studied in the same way. The chemical oxygen demand (COD) of the samples was determined using the dichromate method³⁸ after separation of the solid phase by centrifugation.

3. Results and discussion

Synthesis and characterization of Ag/AgBr/GO

Practically, as shown in Scheme 1, a fast and facile sonochemical route was used to prepare the Ag/AgBr/GO (U) plasmonic photocatalyst with cubic morphology of AgBr. KBr templates were first prepared by injecting a saturated KBr aqueous solution into a GO ethyl alcohol solution at 0 °C. The KBr solubility decreased rapidly from water (25 °C) to absolute ethyl alcohol (0 °C). On the other hand, the oxygenated functional groups, such as hydroxyl, epoxide and carboxyl, on the GO sheets could act as favorable anchoring sites for the nucleation and growth of KBr. Therefore, the KBr crystals were precipitated on the GO surface immediately. The AgNO₃ solution was subsequently added to the KBr dispersions, along with the assistance of PVP as a surfactant to prevent the aggregation of AgBr particles. The ion exchange diffusion reaction between KBr and Ag⁺ in the solution led to the heterogeneous nucleation and continued growth of AgBr on the surface of the GO nanosheet. After 3 h sonication at a temperature of around 5 °C, the AgBr/GO ethanol dispersion was illuminated by sunlight to form Ag/AgBr/GO (U) with the cubic morphology of AgBr.

Scheme 1 Schematic of the formation of the Ag/AgBr/GO (U) photocatalyst with a cubic morphology.

The Fourier transform infrared spectrum (FT-IR) of the Ag/AgBr/GO (U) nanocomposite and original GO was examined to validate the synergistic effect between the Ag/AgBr nanoparticles and graphene oxide nanosheets. As seen in Fig. 1 the carbonyl stretching band at 1731 cm⁻¹ exhibited by the original GO shifts to the lower wavenumber of 1722 cm⁻¹.³⁹ Furthermore, the intensity of the characteristic bands in GO, such as C–O and C–OH, became weaker in the Ag/AgBr/GO nanocomposite. This result verifies the evident interactions between Ag/AgBr and the graphene oxide sheets and suggests the successful hybridization between these two components.

Fig. 1 FTIR spectra of GO and Ag/AgBr/GO (U).

The crystal structure of the obtained Ag/AgBr/GO (U) plasmonic photocatalyst was characterized by X-ray diffraction (XRD). Fig. 2 clearly indicates that the peaks at 26.7°, 31.0°, 44.3°, 52.5°, 55.0°, 64.5° and 73.3° are attributed to the crystal planes of cubic AgBr (JCPDS no. 06-0438), and the peaks at 38.2°, 44.3°, 64.5°, and 77.9° are attributed to the diffractions of metallic Ag (JCPDS no. 04-0783). In the enlarged pattern of Fig. 2a and b, Ag/AgBr and Ag/AgBr/GO (U) exhibited a diffraction peak centered at 2θ = 38.2°, which is indexed to the Ag (111) plane reflection.⁴⁰ However, no obvious peak for GO is observed in the composites via XRD (Fig. 2a and b). This is due to the small amount of loaded GO, which has a low atomic number and cannot be resolved by XRD.⁴¹

Fig. 2 XRD spectra of (a) Ag/ABr/GO (U) (b) Ag/AgBr (c) GO (d) and (e) inset: enlarged XRD patterns at the peak position of the (111) plane of cubic-phase Ag⁰.

Furthermore, the structural change and the interaction between Ag/AgBr and GO could also be disclosed by the Raman spectra, as shown in Fig. 3. Two characteristic peaks of the graphitic material, namely, the D and G band, were also observed in Ag/AgBr/GO (U) at 1350 cm⁻¹ and 1590 cm⁻¹, respectively. The G band of GO which is located at 1600 cm⁻¹ shifts to the lower frequency in Ag/AgBr/GO (U). This result solidly confirms the interaction of AgBr with GO because the Raman spectrum of GO shifts to lower frequencies (softening) when hybridized with an electron donor component.⁴² In addition, the intensity ratio of the D-band to G-band (I_D/I_G) in the Raman spectrum increased from 1.02 in GO to 1.16 in Ag/AgBr/GO, which indicates a decrease in the average size of the in-plane sp² domains of C atoms in the as prepared Ag/AgBr/GO (U) nanocomposite.¹¹ These results indicate that charge transfer and the recombination of electron–hole pairs could be essentially facilitated and suppressed, respectively, thus leading to the enhanced photocatalytic activity of Ag/AgBr/GO (U).

Fig. 3 Raman spectra of GO and Ag/AgBr/GO (U).

For visible light and sunlight energized catalysts, it is required that they display distinct absorptions in the visible region. In general, pure AgBr can absorb light with a wavelength shorter than 470 nm in the ultraviolet region but has negligible absorption in the visible region.⁴³ The UV-visible diffuse reflectance spectra (DRS) of Ag/AgBr and Ag/AgBr/GO (U) synthesized by ultrasound and conventional methods are illustrated in Fig. 4. It can be seen that all the samples involving the Ag species display strong absorption both in the ultraviolet and visible regions. This suggests the existence of metallic Ag species in all of our samples, which arose from the plasmon resonance absorptions in the visible region. The absorption spectra of the Ag/AgBr/GO (U) nanocomposites display the distinct absorption of GO at ca. 238 nm, which confirms the existence of GO sheets in these nanocomposite.⁴⁴

Fig. 4 UV-vis diffusive reflection spectra of Ag/AgBr/GO (U), Ag/AgBr, and Ag/AgBr/GO (C).

Compared with Ag/AgBr/GO (C), the Ag/AgBr/GO (U) sample shows a higher absorption of visible light in the region from 450 nm to 800 nm. This can be attributed to the SPR effect of silver nanoparticles deposited on AgBr cubic particles. This is a consequence of the enhancement of the local electromagnetic field due to the collective response of electrons at specific wavelengths. Therefore, the as-prepared Ag/AgBr/GO (U) may have the potential to achieve high photocatalytic activity in the entire sunlight region.⁴⁵

The morphologies of the nanostructures were characterized by (SEM), as shown in Fig. 5. It can be seen that the nanoparticles with a cubic morphology and average size of about 400 nm could be obtained in the case of the Ag/AgBr nanospecies. Well-defined cubic nanoparticles, whose average size is ca. 170 nm and whose surface is distinctly enwrapped with gauze-like GO nanosheets, could be obtained in the case of the Ag/AgBr/GO (U) nanocomposites, as shown in Fig. 6. The smaller size of the Ag/AgBr nanoparticles in the Ag/AgBr/GO (U) nanocomposites compared with that of the corresponding Ag/AgBr without GO might be due to the existence of GO nanosheets and the application of ultrasonic irradiation. The cavitation phenomena result in shockwaves and microjets, which cause the particles to fragment, and GO might be able to further improve the dispersability of particles in the solution.

Fig. 5 SEM image of cubic Ag/AgBr.

Fig. 6 SEM image of Ag/AgBr/GO (U), inset: Ag/AgBr/GO (U) with high magnification.

Photocatalytic activities

Effective parameters. Typically, before sun light irradiation and the beginning photocatalytic decomposition, the solution was magnetically stirred in the dark for different interval times to attain adsorption–desorption equilibrium between the pollutant and the Ag/AgBr/GO (U) photocatalyst. The experiment was carried out at different times and 30 min was required to reach equilibrium (Fig. S1 (see ESI†)). With an increase in time of remaining in dark, no obvious difference in adsorption was observed after 30 min. This is due to the saturation of the active sites of the photocatalyst with pollutant. As indicated in Fig. 7a, 45% of DCF was adsorbed in the dark with 0.030 g of catalyst after 30 min. This result confirms the high specific surface area of GO, which caused the high efficiency of DCF adsorption on the photocatalyst. Ag/AgBr/GO (U) is a photocatalyst, which needs visible light to generate oxidative species (electrons, holes, OH˙, …) for DCF degradation. Therefore, under light irradiation (Fig. 7b), about 95% of DCF was degraded. With 0.015 g catalyst, approximately 25% of DCF was adsorbed by the catalyst in the dark and 65% of DCF was degraded after 6 min. With an increase in the dosage value to 0.040 g of catalyst, the results are similar to 0.030 g. By increasing the amount of catalyst to 0.040 g, the total active sites on the surface of catalyst increase but a decrease in the penetration of sunlight irradiation can occur due to the increase in turbidity of the suspension.^46,47 These results confirm that the lowest adsorption and degradation was obtained with 0.015 g of Ag/AgBr/GO (U) nanocomposite and the optimum was obtained with 0.030 g. Hence, all experiments were continued with 0.030 g of photocatalyst in 25 mL of DCF (25 mg L⁻¹). In this case, the removal of DCF from the aqueous solution by Ag/AgBr/GO (U) was enhanced, which is due to the large surface area of the nanocomposite.

Fig. 7 Effect of catalyst loading on (a) adsorption efficiency in the dark and (b) degradation efficiency of DCF under light (C₀ = 25 (mg L⁻¹), pH = 6.2, time of irradiation = 6 min, temperature = 17–22 °C).

Period of time for sunlight irradiation were examined in the degradation of DCF and the results are shown in Fig. S2 (see ESI†).

The effect of solution pH on the extent of degradation of DCF was investigated by varying the initial pH over the range of 2–9 at optimized conditions. The UV-vis absorption of DCF in the mentioned range of pH is shown in Fig. S3a.† The pK_a value of diclofenac sodium is 4.35 ± 0.2. DCF exists in its molecular form at a pH lower than its pK_a value, while at higher pH, it exists in its ionic form.⁴⁸ Hence, at lower pH due to their hydrophobic nature, diclofenac molecules can precipitate and the DCF concentration decreases in solution. It is indicated that in acidic media (pH = 2, 3 and 4), DCF has a molecular form and its concentration decreases to 40% in solution automatically (Fig. S3b†). Investigation of the pH effect was done at pH = 5, 6, 9 and the results are shown in Fig. S2.† The natural pH of DCF (pH = 6.2) was chosen to perform the photocatalytic experiments.

Comparison of samples in the removal of DCF

The activity of the Ag/AgBr/GO (U) nanocomposite was examined through the photocatalytic degradation of DCF (25 mg L⁻¹), which is a pharmaceutical pollutant, under solar light irradiation and compared with Ag/AgBr. Obviously, the synthesized Ag/AgBr/GO (U) showed the highest photocatalytic activity among all the samples under solar light. In the Ag/AgBr/GO sample, GO has a key role in the adsorption of the pollutant. The GO-involved nanostructures display a distinctly higher adsorptive ability for DCF than Ag/AgBr. This is due to the distinct intermolecular π–π interactions between the GO nanosheets and pollutant molecules. The enhancement of catalytic activity upon the hybridization of GO is partially due to the smaller size of Ag/AgBr/GO, and the excellent adsorptive capacity of Ag/AgBr/GO with respect to DCF molecules. At the same time, the catalytic enhancement is also partially attributed to the strengthened charge transfer and the suppressed recombination of electron–hole pairs in Ag/AgBr/GO.⁴⁵ Fig. 8a shows that the degradation of DCF on Ag/AgBr/GO (U) is fast, since DCF elimination is completed in 6 min and the peak intensity decreased rapidly at the wavelength of 275 nm (as shown in Fig. 8b). As shown in Table 1, in comparison with other semiconductors, the present nanocomposite showed an improved photocatalytic activity for DCF decomposition.^49–52

Fig. 8 (a) Degradation curves of DCF (25 mg L⁻¹) over Ag/AgBr/GO (U), Ag/AgBr photocatalyst and the blank. (b) Variations of the UV-vis spectrum of DCF vs. the corresponding degradation time.

On the other hand, renewable catalytic activity or stability is another important factor for evaluation. To show the stability of Ag/AgBr/GO (U), cycling catalytic performance was performed 4 times. In each cycle, the Ag/AgBr/GO (U) nanocomposite was added to 25 mL fresh DCF (25 mg L⁻¹) solution. After use, the Ag/AgBr/GO (U) nanocomposite was separated from the solution. Then, the collected sample was repeatedly used in successive cycles.

As shown in Fig. 9a, the photocatalytic activity of the as-prepared catalyst was still maintained at a high level even in the 4th cycle. All these results indicate that the as-prepared Ag/AgBr/GO (U) photocatalyst with cubic morphology is highly stable and active.

Fig. 9 (a) Cyclic photodegradation of DCF solutions in the presence of Ag/AgBr/GO (U) for four cycles. (b) COD variation of DCF solution versus time in solar radiation.

The photocatalytic mineralization of DCF was followed by measuring the COD during the process. DCF in solution could be photocatalytically degraded in 6 min, and the reduction of COD followed a gradual decrease and reached 93% in 6 min (Fig. 9b). In fact, the adsorption and degradation of DCF were carried out simultaneously. When the pollutant on the catalyst site was converted to inorganic species under solar radiation, the DCF in solution was replaced. Light oxidation continued until the total adsorbed DCF was converted to mineral species.

4. Conclusion

In summary, a novel, stable and highly active Ag/AgBr/GO photocatalyst, which has the cubic morphology of AgBr, was prepared via a facile and fast method via ultrasonic irradiation. High pressure and temperature, microjets and shockwaves result in cavitation phenomena of ultrasound irradiation, which resulted in an increase in the speed of the reaction and decrease in the size of particles, which has high dispersion and high contact of particles on GO nanosheets. Subsequently, a photo-reduction process was used to produce Ag nanoparticles on the surface of AgBr/GO. The as-prepared Ag/AgBr/GO (U) had well-defined cubic AgBr particles with a size smaller than cubic Ag/AgBr without GO. The high specific surface area of GO has an essential role to improve the photocatalytic activity efficiency. The photocatalytic activities of the sono-synthesized Ag/AgBr/GO (U) and cubic Ag/AgBr were compared via the decomposition of DCF under solar light in ambient conditions. In addition, some effective parameters in photocatalytic performance, such as the effect of the dark, amount of catalyst, pH of medium and time of sun light irradiation, were investigated. The experimental results confirmed that the sono-synthesized Ag/AgBr/GO (U) nanocomposite exhibited the highest photocatalytic activity in comparison with others. Moreover, the photocatalyst maintains a high level of activity even after 4 cycles of use.

Therefore, the excellent photocatalytic performance of Ag/AgBr/GO (U), simplicity of the synthetic process and use of a low energy source are the most important factors of this nanocomposite. This photocatalyst is a promising material, which can be applied effectively in the removal of pharmaceutical pollutants such as DCF from aqueous media.

Acknowledgements

The support by the Ferdowsi University of Mashhad (Research and Technology) for this study (code 3/29791, date 2014/01/26) is appreciated.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ra16814g

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