One-pot synthesis of Ag–Cu–Cu2O/C nanocomposites derived from a metal–organic framework as a photocatalyst for borylation of aryl halide

Mixed metal–metal oxide/C (Ag–Cu–Cu₂O/C) nanocomposites were synthesized by the heat treatment of a metal–organic framework under a N₂ flow using the one-pot synthesis method. The as-prepared nanocomposites were characterized using a range of techniques, such as TEM, elemental mapping, XRD, N₂ sorption, UV-Vis DRS, and XPS. The nanoparticles were successfully formed with high dispersion in porous carbon materials and high crystallinity based on the analysis results. The Ag–Cu–Cu₂O/C nanocomposites (35 nm) showed high photocatalytic activity and good recyclability toward the borylation of aryl halides under a xenon arc lamp. This result can enhance the interest in photocatalysis for various applications, particularly in organic reactions, using a simple and efficient synthesis method.

Ag–Cu–Cu₂O/C nanocomposites derived from metal–organic framework through one-pot thermal reduction method were synthesized. The material exhibits high catalytic activity in the borylation of aryl halide under xenon lamp condition across 7 cycles, with no yield decrease.     

A visible light active,carbon–nitrogen–sulfur co-doped TiO2/g-C3N4 Z-scheme heterojunction as an effective photocatalyst to remove dye pollutants

Heterojunction formation and heteroatom doping could be viewed as promising strategies for constructing composite photocatalysts with high visible light catalytic activity. In this work, we fabricated a carbon, nitrogen and sulfur co-doped TiO₂/g-C₃N₄ (CNS-TiO₂/g-C₃N₄) Z-scheme heterojunction photocatalyst composite via one-step hydrothermal and calcination methods. Compared with pure TiO₂ and g-C₃N₄, the CNS-TiO₂/g-C₃N₄ Z-scheme heterojunction photocatalyst possessed excellent degradation performance under visible light irradiation. Due to the formation of the Z-scheme heterostructure, the utilization rate of the photogenerated electrons–holes generated by the catalyst was increased, which enhanced the catalytic activity. Moreover, the heteroatom doping (C, N and S) could efficiently tailor the band gap of TiO₂ and facilitate electron transition, contributing to enhancing the degradation ability under visible light. The CNS-TiO₂/g-C₃N₄-2 exhibited a superior photocatalytic degradation efficiency (k = 0.069 min⁻¹) for methyl orange dye (MO), which is higher than those of pure TiO₂ (k = 0.001 min⁻¹) and g-C₃N₄ (k = 0.012 min⁻¹), showing excellent photocatalytic activity against organic pollutants.

The CNS-TiO₂/g-C₃N₄ photocatalyst with excellent visible light catalytic activity was successfully manufactured, benefiting from the construction of the Z-scheme heterojunction and the co-doping of heteroatoms (C, N and S).     

Novel TiO2/GO/CuFe2O4 nanocomposite: a magnetic,reusable and visible-light-driven photocatalyst for efficient photocatalytic removal of chlorinated pesticides from wastewater

A TiO₂/GO/CuFe₂O₄ heterostructure photocatalyst is fabricated by a simple and low-cost ball-milling pathway for enhancing the photocatalytic degradation of chlorinated pesticides under UV light irradiation. Based on the advantages of graphene oxide, TiO₂, and CuFe₂O₄, the nanocomposite exhibited visible light absorption, magnetic properties, and adsorption capacity. Integrated analyses using XRD, SEM, TEM, and UV-visible techniques demonstrated that the nanocomposite exhibited a well-defined crystalline phase, sizes of 10–15 nm, and evincing a visible light absorption feature with an optical bandgap energy of 2.4 eV. The photocatalytic degradations of 17 different chlorinated pesticides (persistent organic pollutants) were assayed using the prepared photocatalyst. The photocatalytic activity of the nanocomposite generated almost 96.5% photocatalytic removal efficiency of typical pesticide DDE from water under UV irradiation. The superior photocatalytic performance was exhibited by the TiO₂/GO/CuFeO₄ catalyst owing to its high adsorption performance and separation efficiency of photo-generated carriers. The photocatalyst was examined in 5 cycles for treating uncolored pesticides with purposeful separation using an external magnetic field.

A TiO₂/GO/CuFe₂O₄ heterostructure photocatalyst is fabricated by a simple and low cost ball milling pathway for enhancing the photocatalytic degradation of chlorinated pesticides under UV light irradiation.     

Versatility of CoPcS in CoPcS/TiO2 for MB degradation: photosensitization,charge separation and oxygen activation

In this report, a composite photocatalyst consisting of cobalt phthalocyanine sulfate (CoPcS) and TiO₂ was prepared by a facile synthesis. Careful characterizations and measurements indicate a covalent grafting of CoPcS onto TiO₂ through Ti–O–S linkages, acquiring an intimate heterojunction between TiO₂ and CoPcS. The obtained composite was evaluated for its photocatalytic activity toward the degradation of methyl blue (MB) under visible light irradiation. The evaluation showed a significantly enhanced degradation rate of MB by CoPcS/TiO₂. The improved photocatalytic performance of CoPcS/TiO₂ was attributed to the photosensitization of TiO₂ by CoPcS, charge separation by electron transfer at the interface of the heterojunction formed between CoPcS and TiO₂, and oxygen activation via CoPcS. A synergetic mechanism in improving the photocatalytic performance of TiO₂ by CoPcS was investigated.

In this report, a composite photocatalyst consisting of cobalt phthalocyanine sulfate (CoPcS) and TiO₂ was prepared by a facile synthesis.     

Fast photocatalytic degradation of dyes using low-power laser-fabricated Cu2O–Cu nanocomposites

In this study, we report a simple method to controllably synthesize Cu₂O–Cu nanocomposites by using a low-power CO₂ laser, and application of these nanomaterials for photocatalytic degradation of methylene blue (MB). Our experiments demonstrate that efficient tailoring of the Cu₂O–Cu nanocomposites can be realized by accurate control and optimization of the ambient parameters, such as laser energy and NaOH concentration. Compared to hydrothermally fabricated Cu₂O–Cu catalysts, the laser-reduced composites exhibit better visible-light photocatalytic activity for MB degradation, which could be attributed to the formation of special catalytically active structures on the nanocomposite surface. Under the conditions of 10 mA laser irradiation and 5 M NaOH addition, the fabricated Cu₂O–Cu composites had the highest catalytic activity. The degradation rate of MB is 90.10% after visible-light irradiation for 50 min under the optimum conditions. The as-synthesized Cu₂O–Cu composites showed selective dye degradation, and exhibit relatively higher photocatalytic efficiency for positively charged dyes. This work could lead to facile synthesis of high-performance photocatalysts for fast removal of environmentally hazardous dyes from aqueous solution.

Facile synthesis of Cu₂O–Cu nanocomposites by using a low-power CO₂ laser was realized, and the fabricated nanomaterials showed excellent photocatalytic activity for the degradation of various dyes.     

A hierarchical Ca/TiO2/NH2-MIL-125 nanocomposite photocatalyst for solar visible light induced photodegradation of organic dye pollutants in water

In this study, for the first time, the Ca/TiO₂/NH₂-MIL-125 nanocomposite photocatalyst was synthesized for the purpose of photodegradation of Methyl Orange (MO) and Rhodamine B (RhB) dyes under visible light irradiation. The structural and chemical properties of the nanocomposite photocatalyst were characterized through FTIR, XRD, TGA, PL, XPS, ICP-OES and UV-DRS. For the photodegradation efficiency analysis, the effect of pH (3, 5, 7, 9, and 11), photocatalyst dosage (0.1, 0.2, 0.4, 0.6, and 0.8 g L⁻¹), dye concentration (1–40 mg L⁻¹), and contact time (10–120 min) was precisely evaluated. The largest photodegradation efficiency for RhB and MO dye models was 82.87% and 86.22%, respectively, that was obtained under optimal conditions in terms of pH and photocatalyst dosage and for Ca(30%)/TiO₂/NH₂-MIL-125. The photodegradation process of the dyes complied well with the first-order kinetic model. Moreover, the nanocomposite photocatalyst showed consistent photodegradation efficiency and after 6 successive cycles with fresh dye solutions, it could still perform comparably well. Taken together, Ca/TiO₂/NH₂-MIL-125 photocatalyst is able to show a high photodegradation efficiency for dye pollutants and optimum stability and reusability.

In this study, for the first time, the Ca/TiO₂/NH₂-MIL-125 nanocomposite photocatalyst was synthesized for the purpose of photodegradation of Methyl Orange (MO) and Rhodamine B (RhB) dyes under visible light irradiation.     

Efficient photocatalysis with graphene oxide/Ag/Ag2S–TiO2 nanocomposites under visible light irradiation

Lack of visible light response and low quantum yield hinder the practical application of TiO₂ as a high-performance photocatalyst. Herein, we present a rational design of TiO₂ nanorod arrays (NRAs) decorated with Ag/Ag₂S nanoparticles (NPs) synthesized through successive ion layer adsorption and reaction (SILAR) and covered by graphene oxide (GO) at room temperature. Ag/Ag₂S NPs with uniform sizes are well-dispersed on the TiO₂ nanorods (NRs) as evidenced by electron microscopic analyses. The photocatalyst GO/Ag/Ag₂S decorated TiO₂ NRAs shows much higher visible light absorption response, which leads to remarkably enhanced photocatalytic activities on both dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 600% higher than that of pure TiO₂ sample under visible light. This remarkable enhancement can be attributed to a synergy of electron-sink function and surface plasmon resonance (SPR) of Ag NPs, band matching of Ag₂S NPs, and rapid charge carrier transport by GO, which significantly improves charge separation of the photoexcited TiO₂. The photocurrent density of GO/Ag/Ag₂S–TiO₂ NRAs reached to maximum (i.e. 6.77 mA cm⁻²vs. 0 V). Our study proves that the rational design of composite nanostructures enhances the photocatalytic activity under visible light, and efficiently utilizes the complete solar spectrum for pollutant degradation.

The photocatalytic reaction efficiency of GO/Ag/Ag₂S–TiO₂ nanorod arrays is 600% higher than that of a pure TiO₂ sample under visible light.     

A green route for the cross-coupling of azide anions with aryl halides under both base and ligand-free conditions: exceptional performance of a Cu2O–CuO–Cu–C nanocomposite

A convenient, inexpensive and effective route for the preparation of a Cu₂O–CuO–Cu–C nanocomposite is described here by applying Cu(ii) as a source of copper. Characterization of the nanocomposite was performed with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX). Analysis of the data showed that the particles of the nanocomposite are uniformly distributed and show high catalytic activity in the cross-coupling of sodium azide with various aryl iodides and bromides. This nanocomposite has a high level of performance, and even led to the synthesis of the products at room temperature. In addition, this is the first report of the synthesis of aryl azides under both base- and ligand-free conditions. For the first time, both ligand- and base-free conditions were applied for the synthesis of aryl azides, which implies exceptional performance of the Cu₂O–CuO–Cu–C nanocomposite. Simultaneous removal of the base and ligand in a green solvent is the main advantage of this reaction. Unfortunately, aryl bromides and aryl iodides with electron-withdrawing functional groups in their scaffold did not give the desired aryl azides.

Ligand-free and base-free conditions were used for the preparation of aryl azides using the cross-coupling of sodium azide and aryl halides catalysed by Cu₂O–CuO–Cu–C.     

Preparation of S–N co-doped CoFe2O4@rGO@TiO2 nanoparticles and their superior UV-Vis light photocatalytic activities

A S–N co-doped CoFe₂O₄@rGO@TiO₂ (CFGT-S/N) nanocomposite was successfully synthesized via a facile vapor-thermal method. XRD, XPS, FT-IR and FETEM results confirmed that N and S were co-doped into the lattice of TiO₂. Photocatalytic tests indicated that CFGT-S/N exhibited excellent UV-Vis photocatalytic activity for decompositions of different organic dyes, including methyl orange (MO), rhodamine B (RhB) and methylene blue (MB). Particularly, the photocatalytic degradation rate of MO was about 33% higher than that when using P25 under visible light irradiation. The higher UV-Vis light photocatalytic activity of CFGT-S/N can be attributed to the synergetic effects of the strong absorption of visible light, the narrow band gap, improved separation of photo-generated electron/hole pairs, and the enhancement of the enrichment of pollutant dye molecules by S, N co-doping, CoFe₂O₄ and rGO. Moreover, this photocatalyst was superparamagnetic, which enables it to be easily recovered by an external magnetic field, and maintained stable photocatalytic efficiency over five cycles. Hence, CFGT-S/N with its highly efficient, recoverable and stable photocatalytic properties shows great potential for environmental treatment.

A magnetic recoverable S–N co-doped CoFe₂O₄@rGO@TiO₂ (CFGT-S/N) nanocomposite was synthesized via a facile vapor-thermal method. CFGT-S/N is an excellent UV-Vis photocatalyst because of the synergetic effects of S, N co-doping, the introduction of CoFe₂O₄ and rGO.     

Highly efficient visible light active Cu–ZnO/S-g-C3N4 nanocomposites for efficient photocatalytic degradation of organic pollutants

The photocatalytic activity of photocatalysts is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺. In the current study, the photocatalytic efficiency of Cu–ZnO/S-g-C₃N₄ (CZS) nanocomposites was investigated against MB dye. The composite materials were designed via chemical co-precipitation method and characterised by important analytical techniques. Distinctive heterojunctions developed between S-g-C₃N₄ and Cu–ZnO in the CZS composite were revealed by TEM. The synthesized composites exhibit a huge number of active sites, a large surface area, a smaller size and better visible light absorption. The considerable enhancement in the photocatalytic activity of CZS nanocomposites might be accredited to the decay in the e–h pair recombination rate and a red shift in the visible region, as observed by PL and optical analysis, respectively. Furthermore, the metal (Cu) doping into the S-g-C₃N₄/ZnO matrix created exemplary interfaces between ZnO and S-g-C₃N₄, and maximized the photocatalytic activity of CZS nanocomposites. In particular, CZS nanocomposites synthesized by integrating 25% S-g-C₃N₄ with 4% Cu–ZnO (CZS-25 NCs) exhibited the 100% photocatalytic degradation of MB in 60 minutes under sunlight irradiation. After six cycles, the photocatalytic stability of CZS-25 NCs was excellent. Likewise, a plausible MB degradation mechanism is proposed over CZS-25 NCs based on photoluminescence and reactive species scavenger test observation. The current research supports the design of novel composites for the photocatalytic disintegration of organic contaminants.

The photocatalytic activity of photocatalyst is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺.     

Mechanistic study of N–H- and H–N-codoping of a TiO2 photocatalyst for efficient degradation of benzene under visible light

Non-metal codoping including nitrogen (N) and hydrogen (H) codoping has been emerging as an effective way to improve the performance of anatase TiO₂ in solar cell, fuel conversion and pollutant degradation. However, the mechanism of the synergistic effect of N doping and H doping on TiO₂ is still far from thorough. In this paper, N and H codoped TiO₂ nanoparticles are obtained by N doping in ammonia and then H doping in hydrogen gas, which achieves substantially boosted efficiency and reaction rate in the photocatalytic degradation of benzene under visible light excitation. The superiority of the N–H–TiO₂ photocatalyst was fully elaborated by comparing with H–N–TiO₂, which was obtained by thermal treating in H₂ and then NH₃. The reaction rate of N–H–TiO₂ in the photocatalytic degradation of benzene was nearly 2 times that of H–N–TiO₂, ∼7 times higher than that of pristine TiO₂. Furthermore, the cycling test revealed the high repeatability and stability of the N–H–TiO₂ photocatalyst. The excellent performance N–H–TiO₂ was attributed to an adequate concentration of N_iH_i defects occupying interstitial sites of the TiO₂ structure and a disordered surface layer introduced by annealing in NH₃ and H₂ successively. The synergistic effect of N–H-codoping also increased the separation and migration of electron–hole pairs triggering a photoinduced redox reaction on the surface of TiO₂.

The crystallinity, N_iH_i dopants and disordered surface layer are of importance to N–H–TiO₂ when comparing with the structure and properties of H–N–TiO₂.     

Novel blended catalysts consisting of a TiO2 photocatalyst and an Al2O3 supported Pd–Au bimetallic catalyst for direct dehydrogenative cross-coupling between arenes and tetrahydrofuran

Dehydrogenative cross-coupling (DCC) is a clean methodology to make C–C bonds by using abundant C–H bonds. The blended catalyst, developed in this study, consists of a TiO₂ photocatalyst and an Al₂O₃ supported Pd–Au bimetallic catalyst and shows superior activity to the conventional TiO₂ photocatalyst loaded with the corresponding metal co-catalyst for the direct DCC between various arenes and tetrahydrofuran, with concomitant evolution of hydrogen gas. The reactions were done under mild conditions without consuming any oxidising agent or other additional chemicals. This new approach of separating the photocatalyst and the metal catalyst parts allows their independent modification to improve the overall catalytic performance.

A TiO₂ photocatalyst physically mixed with a supported Pd–Au bimetallic catalyst is more efficient than Pd loaded TiO₂ sample for the photocatalytic DCC between arene and THF.     

Fabrication of Ag2O/WO3 p–n heterojunction composite thin films by magnetron sputtering for visible light photocatalysis

Semiconductor-based nanostructures which are photo-catalytically active upon solar light irradiation were extensively used for environmental remediation due to the potential decomposition of various kinds of pollutants. In this work, we report the preparation of a sustainable thin film composite, i.e. Ag₂O/WO₃ p–n heterojunction, and investigation of its photocatalytic activity. To achieve the composite structure, WO₃/Ag–WO₃ layers were deposited over a quartz substrate by magnetron sputtering at room temperature and subsequently annealed at 823 to 923 K. The thin film structure, morphology, and chemical states were thoroughly characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron spectroscopy, and X-ray photoelectron spectroscopy. The obtained results revealed that the amorphous Ag-doped WO₃ was crystallized into monoclinic WO₃ and Ag₂O, in which nanocrystalline Ag₂O was diffused towards the surface of WO₃. Optical transmittance spectra recorded by UV-vis-NIR spectroscopy revealed that the WO₃/Ag–WO₃ films became transparant in the visible region after annealing at high temperature (873 K and 923 K). The Ag₂O/WO₃ p–n heterojunction composite thin films showed high photocatalytic activity (0.915 × 10⁻³ min⁻¹) under visible light irradiation, which is attributed to the efficiency of effective photogenerated charge-carrier formation and the reduced recombination rate of photogenerated electron–hole pairs. Unlike the powder-based photocatalysts, the reported thin film-based heterojunction photocatalyst could be very sustainable, and cost-effective.

Semiconductor-based nanostructures which are photo-catalytically active upon solar light irradiation were extensively used for environmental remediation due to the potential decomposition of various kinds of pollutants.     

Facile one-pot synthesis of heterostructure SnO2/ZnO photocatalyst for enhanced photocatalytic degradation of organic dye

In this work, heterostructure SnO₂/ZnO nanocomposite photocatalyst was prepared by a straightforward one step polyol method. The resulting photocatalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption analyses, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The results showed that the synthesized SnO₂/ZnO nanocomposites possessed mesoporous wurtzite ZnO and cassiterite SnO₂ nanocrystallites. The photocatalytic activity of the prepared SnO₂/ZnO photocatalyst was investigated by the degradation of methylene blue dye under UV light irradiation. The heterostructure SnO₂/ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue dye than individual SnO₂, ZnO nanomaterials and reference commercial TiO₂ P25. This higher photocatalytic degradation activity was due to enhanced charge separation and subsequently the suppression of charge recombination in the SnO₂/ZnO photocatalyst resulting from band offsets between SnO₂ and ZnO. Finally, these heterostructure SnO₂/ZnO nanocatalysts were stable and could be recycled several times without any appreciable change in degradation rate constant which opens new avenues toward potential industrial applications.

In this work, heterostructure SnO₂/ZnO nanocomposite photocatalyst was prepared by a straightforward one step polyol method.     

A novel n-type CdS nanorods/p-type LaFeO3 heterojunction nanocomposite with enhanced visible-light photocatalytic performance

In this work, a novel n-type CdS nanorods/p-type LaFeO₃ (CdS NRs/LFO) nanocomposite was prepared, for the first time, via a facile solvothermal method. The as-prepared n-CdS NRs/p-LFO nanocomposite was characterized by using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), UV-visible diffuse reflection spectroscopy (DRS), vibrating sample magnetometry (VSM), photoluminescence (PL) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis. All data revealed the attachment of the LFO nanoparticle on the surface of CdS NRs. This novel nanocomposite was applied as a novel visible light photocatalyst for the degradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes under visible-light irradiation. Under optimized conditions, the degradation efficiency was 97.5% for MB, 80% for RhB and 85% for MO in the presence of H₂O₂ and over CdS NRs/LFO nanocomposite. The photocatalytic activity of CdS NRs/LFO was almost 16 and 8 times as high as those of the pristine CdS NRs and pure LFO, respectively. The photocatalytic activity was enhanced mainly due to the high efficiency in separation of electron–hole pairs induced by the remarkable synergistic effects of CdS and LFO semiconductors. After the photocatalytic reaction, the nanocomposite can be easily separated from the reaction solution and reused several times without loss of its photocatalytic activity. Trapping experiments indicated that ·OH radicals were the main reactive species for dye degradation in the present photocatalytic system. On the basis of the experimental results and estimated energy band positions, the mechanism for the enhanced photocatalytic activity was proposed.

A novel n–p CdS nanorods/LaFeO₃ (CdS NRs/LFO) heterojunction nanocomposite was prepared via a solvothermal route and applied as a visible-light photocatalyst for enhanced degradation of organic dye pollutants.     

Synthesis and photocatalytic properties of visible-light-responsive,three-dimensional,flower-like La–TiO2/g-C3N4 heterojunction composites

We prepared a new three-dimensional, flower-like La–TiO₂/g-C₃N₄ (LaTiCN) heterojunction photocatalyst using a solvothermal method. Analysis and characterization were performed by conducting scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform-infrared spectroscopy, ultraviolet-visible spectrophotometry, and nitrogen adsorption and desorption. The prepared g-C₃N₄ nanosheets could reach 100 nm in size and covered the TiO₂ surface. A tightly bound interface formed between the g-C₃N₄ and TiO₂, speeding up the effective transfer of photo-induced electrons. In addition, the incorporation of La³⁺ reduced the electron–hole recombination efficiency. Consequently, the prepared La–TiO₂/g-C₃N₄ composite material exhibited better visible-light catalytic activity than pure TiO₂.

A new visible-light-responsive, three-dimensional, flower-like La–TiO₂/g-C₃N₄ heterojunction photocatalyst was prepared by a solvothermal method.     

Copper–zinc oxide heterojunction catalysts exhibiting enhanced photocatalytic activity prepared by a hybrid deposition method

Heterojunction copper–zinc oxide catalysts were prepared by a hybrid two-step methodology comprising hydrothermal growth of ZnO nanorods (ZnO-NR) followed by deposition of Cu₂O nanoparticles using an advanced gas deposition technique (AGD). The obtained bicatalysts were characterized by SEM, AFM, XRD, XPS, PL and spectrophotometry and revealed well-dispersed and crystalline Cu₂O nanoparticles attached to the ZnO-NR. The adsorption properties and photocatalytic degradation of Orange II dye in water solutions were measured. It was found that the bicatalysts exhibited a conversion rate and quantum yield that both were about 50% higher compared with ZnO-NR alone, which were attributed to the intrinsic electric field created at the p–n junction formed at the Cu₂O/ZnO interface facilitating charge separation of electron–hole pairs formed upon interband photon absorption. The interpretation was evidenced by efficient quenching of characteristic deep level ZnO photoluminescence bands and photoelectron core-level energy shifts. By comparisons with known energy levels in Cu₂O and ZnO, the effect was found to be most pronounced for the non-polar ZnO-NR side facets, which accounted for about 95% of the exposed surface area of the catalyst and hence the majority of dye adsorption. It was also found that the dye adsorption capacity of the ZnO nanorods increased considerably after Cu₂O deposition thereby facilitating the oxidation of the dye. The results imply the possibility of judiciously aligning band edges on structurally controlled and well-connected low-dimensional semiconductor nanostructures using combined two-step synthesis techniques, where in particular vacuum-based techniques such as AGD allow for growth of well-connected nanocrystals with well developed heterojunction interfaces.

Hybrid synthesis of Cu₂O/ZnO nanorod heterojunction exhibiting enhanced interfacial charge transfer and photocatalytic activity comprising hydrothermal synthesis step of ZnO nanorods followed by advanced gas deposition of Cu nanoparticles.     

2D–3D graphene-coated diatomite as a support toward growing ZnO for advanced photocatalytic degradation of methylene blue

In this work, a diatomite@graphene@ZnO (ZGD) photocatalyst was synthesized by chemical vapor deposition and hydrothermal methods and used for the photocatalytic degradation of methylene blue. The characterization of the prepared nanocomposite was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and N₂ adsorption–desorption techniques. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) showed that the prepared ZGD photocatalyst enhanced the absorption of visible light and induced a red-shift. Photoluminescence spectroscopy (PL) revealed that the recombination of electron and hole pairs can be effectively suppressed. Besides, the synergistic effect of diatomite and graphene avoids the agglomeration of ZnO, increases the number of surface adsorption sites, and limits the electron transport, consequently improving the photocatalytic activity of ZnO. When ZGD-3 was UV-irradiated (λ = 663 nm) for 90 minutes, the degradation effectiveness of methylene blue (MB) was 100%. After the fifth repetition, the photocatalytic degradation efficiency was always greater than 95%. Simply put, the ZGD nanocatalyst can be used as an efficient photocatalyst for dye wastewater treatment.

In this work, a diatomite@graphene@ZnO (ZGD) photocatalyst was synthesized by chemical vapor deposition and hydrothermal methods and used for the photocatalytic degradation of methylene blue.     

Hybrid BiOBr/UiO-66-NH2 composite with enhanced visible-light driven photocatalytic activity toward RhB dye degradation

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years. In this work, a highly active, visible light photocatalyst BiOBr/UiO-66-NH₂ hybrid composite was successfully prepared by introducing various amounts of UiO-66-NH₂ with BiOBr through a co-precipitation method. The composites were applied for the photocatalytic degradation of RhB (rhodamine B) dye. The developed BiOBr/UiO-66-NH₂ composites exhibited higher photocatalytic activity than the pristine material. In RhB degradation experiments the hybrid composite with 15 wt% of UiO-66-NH₂ shows degradation efficiency conversion of 83% within two hours under visible light irradiation. The high photodegradation efficiency of BUN-15 could be ascribed to efficient interfacial charge transfer at the heterojunction and the synergistic effect between BiOBr/UiO-66-NH₂. In addition, an active species trapping experiment confirmed that photo-generated hole⁺ and O₂⁻ radicals are the major species involved in RhB degradation under visible light.

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years.     

Preparation and characterization of Fe3O4@SiO2@TiO2–Co/rGO magnetic visible light photocatalyst for water treatment

In this work, Fe₃O₄@SiO₂@TiO₂–Co/rGO magnetic photocatalyst was successfully prepared by a sol–gel method and a hydrothermal method. The crystalline structure and performance of the resulting catalyst have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and ultraviolet-visible light (UV-Vis) spectroscopy. The magnetic photocatalyst consists of Fe₃O₄@SiO₂@TiO₂–Co active particles and rGO carriers. The active particles have a double-shell core–shell structure with a size of about 500 nm and are supported on the rGO lamellae. TiO₂ doping with a small amount of metal Co and rGO can significantly improve the catalytic effect of magnetic photocatalyst, and rGO can also significantly improve the adsorption of pollutants by magnetic photocatalyst. The catalyst exhibited high photocatalytic activity in the degradation of methylene blue (MB) under visible light. 92.41% of this ability was retained after five times of repetitive use under the same conditions. The magnetic photocatalyst is easy to recover, and a recovery rate of 93.88% is still maintained after repeated use for 5 times.

With its low cost, high photocatalytic activity, high chemical stability and easy magnetic separation, Fe₃O₄@SiO₂@TiO₂–Co/rGO magnetic photocatalyst has a good application potential.