Synthesis and photoactivity of nanostructured CdS–TiO2 composite catalysts

Fabrication, characterization, and performance evaluation of Bi2WO6/TiO2/Fe3O4 photocatalyst responding to visible light for enhancing bisphenol A degradation

A novel magnetic Bi₂WO₆/TiO₂/Fe₃O₄ photocatalyst was synthesized by a hydrothermal approach. The pattern, structure, elemental composition, light-absorbing properties, and magnetism of Bi₂WO₆/TiO₂/Fe₃O₄ were characterized and analyzed. The performance, influencing factors, and mechanism of Bi₂WO₆/TiO₂/Fe₃O₄ towards bisphenol A (BPA) degradation were investigated and deduced. BPA removal up to 95% was achieved with the addition of 1.25 g/L Bi/Ti/Fe2 (molar ratio of Bi₂WO₆:TiO₂:Fe₃O₄ = 2:1:0.17) in the solution containing 10 mg/L BPA at pH 5.6. The performance of Bi/Ti/Fe2 was stable for five cycles at least after extracted from the reacted solution by magnet. Photoexcited h⁺, •OH, and •O₂^- formed in the reaction mainly contributed to BPA degradation. The Bi/Ti/Fe2 composite was composed of a three-layer petal structure from outside to inside to be Bi₂WO₆, TiO₂, and Fe₃O₄. This structure was conducive in forming a heterojunction between TiO₂ and Bi₂WO₆, inhibiting the merging of photoexcited e^- and h⁺, and improving the photocatalytic efficiency.

Biomass Photoreforming for Hydrogen Production over Hierarchical 3DOM TiO2-Au-CdS

Photocatalytic hydrogen production is a promising route to the provision of sustainable and green energy. However, the excess addition of traditional electron donors as the sacrificial agents to consume photogenerated holes greatly reduces the feasibility of this approach for commercialization. Herein, considering the abundant hydroxyl groups in cellulose, the major component of biomass, we adopted glucose (a component unit of cellulose), cellobiose (a structure unit of cellulose) and dissolving pulp (a pretreated cellulose) as electron donors for photocatalytic hydrogen production over a TiO2-Au-CdS material. The well-designed ternary TiO2-Au-CdS possesses a hierarchical three-dimensional ordered macroporous (3DOM) structure, which not only benefits light harvesting but can also facilitate mass diffusion to boost the reaction kinetics. As expected, the fabricated photocatalyst exhibits considerable hydrogen production from glucose (645.1 μmol·h−1·g−1), while the hydrogen production rates gradually decrease with the increased complexity in structure from cellobiose (273.9 μmol·h−1·g−1) to dissolving pulp (79.7 μmol·h−1·g−1). Other gaseous components such as CO and CH4 are also produced, indicating the partial conversion of biomass during the photoreforming process. This work demonstrates the feasibility of sustainable hydrogen production from biomass by photoreforming with a rational photocatalyst design.

The photocatalytic properties and construction of a WS2/MoS2/CdS heterojunction

The as-prepared WS2/MoS2/CdS composite heterojunction semiconductor exhibited high photocatalytic activity when degrading organic pollutants under visible light illumination.

Metal-free n/n-junctioned graphitic carbon nitride (g-C3N4): a study to elucidate its charge transfer mechanism and application for environmental remediation

Graphitic carbon nitride (g-C₃N₄) has been regarded as a promising visible light-driven photocatalyst ascribable to its tailorable structures, thermal stability and chemical inertness. Enhanced photocatalytic activity is achievable by the construction of homojunction nanocomposites to reduce the undesired recombination of photogenerated charge carriers. In the present work, a novel g-C₃N₄/g-C₃N₄ metal-free homojunction photocatalyst was synthesized via hydrothermal polymerization. The g-C₃N₄/g-C₃N₄ derived from urea and thiourea demonstrated admirable photocatalytic activity towards rhodamine B (RhB) degradation upon irradiation of an 18 W LED light. The viability of the photoreaction with a low-powered excitation source highlighted the economic and environmental benefits of the process. The optimal g-C₃N₄/g-C₃N₄ homojunction photocatalyst exhibited a 2- and 1.8-fold increase in efficiency in relative to pristine g-C₃N₄ derived from urea and thiourea respectively. The enhanced photocatalytic performance is credited to the improved interfacial transfer and separation of electron-hole pairs across the homojunction interface. Furthermore, an excellent photochemical stability and durability is displayed by g-C₃N₄/g-C₃N₄ after three consecutive cycles. In addition, a plausible photocatalytic mechanism was proposed based on various scavenging tests. Overall, experimental results generated from this study is expected to intrigue novel research inspirations in developing metal-free homojunction photocatalysts to be feasible for large-scale wastewater treatment without compromising economically. Graphical abstract.

Magnetically Recoverable TiO2/SiO2/γ-Fe2O3/rGO Composite with Significantly Enhanced UV-Visible Light Photocatalytic Activity

In this paper, we report the preparation of a new composite (TiO₂/SiO₂/γ-Fe₂O₃/rGO) with a high photocatalytic efficiency. The properties of the composite were examined by different analyses, including X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), UV-Visible light diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman, vibrating-sample magnetometer (VSM), and nitrogen gas physisorption (BET) studies. The photocatalytic efficiency of the proposed composite was evaluated by the degradation of methylene blue under UV and visible light, and the results were compared with titanium dioxide (TiO₂), where degradation increased from 30% to 84% and 4% to 66% under UV and visible light, respectively. The significant increase in photocatalytic activity may be explained by the higher adsorption of dye on the surface of the composite and the higher separation and transfer of charge carriers, which in turn promote active sites and photocatalytic efficiency.

One-pot preparation of hierarchical Cu2O hollow spheres for improved visible-light photocatalytic properties

As visible light photocatalysts, narrow bandgap semiconductors can effectively convert solar energy to chemical energy, exhibiting potential applications in alleviating energy shortage and environmental pollution. Cu₂O hollow spheres with a narrow band gap and uniform hierarchical structures have been fabricated in a controlled way. The one-pot solvothermal method without any template is simple and facile. The morphologies, crystal structures, composition, specific surface areas, and optical and photoelectric properties of the products were analyzed by various techniques. The hollow and solid Cu₂O spheres could be fabricated by controlling the reaction time, and a possible growth process of the Cu₂O hollow spheres was revealed. The degradation of methyl orange (MO) was used to investigate the visible-light catalytic properties of the Cu₂O samples. More than 90% of MO is degraded under visible light illumination of 20 min, exhibiting a quick catalytic reaction. The rate constant of the Cu₂O hollow spheres was 2.54 times and 46.6 times larger than those of the Cu₂O solid spheres and commercial Cu₂O powder, respectively. The possible photocatalytic mechanism of MO was revealed over Cu₂O hollow spheres through the detection of active species. The as-prepared Cu₂O hollow spheres display improved visible-light catalytic activity and stability, indicating their potential application in wastewater treatment.

As visible light photocatalysts, narrow bandgap semiconductors can effectively convert solar energy to chemical energy, exhibiting potential applications in alleviating energy shortage and environmental pollution.

Construction of Ag3PO4/SnO2 Heterojunction on Carbon Cloth with Enhanced Visible Light Photocatalytic Degradation

In this study, the Ag3PO4/SnO2 heterojunction on carbon cloth (Ag3PO4/SnO2/CC) was successfully fabricated via a facile two-step process. The results showed that the Ag3PO4/SnO2/CC heterojunction exhibited a remarkable photocatalytic performance for the degradation of Rhodamine B (RhB) and methylene blue (MB), under visible light irradiation. The calculated k values for the degradation of RhB and MB over Ag3PO4/SnO2/CC are 0.04716 min−1 and 0.04916 min−1, which are higher than those calculated for the reactions over Ag3PO4/SnO2, Ag3PO4/CC and SnO2/CC, respectively. The enhanced photocatalytic activity could mainly be attributed to the improved separation efficiency of photogenerated electron-hole pairs, after the formation of the Ag3PO4/SnO2/CC heterojunction. Moreover, carbon cloth with a large specific surface area and excellent conductivity was used as the substrate, which helped to increase the contact area of dye solution with photocatalysts and the rapid transfer of photogenerated electrons. Notably, when compared with the powder catalyst, the catalysts supported on carbon cloth are easier to quickly recycle from the pollutant solution, thereby reducing the probability of recontamination.

Role of Nanomaterials in the Treatment of Wastewater: A Review

Water is an essential part of life and its availability is important for all living creatures. On the other side, the world is suffering from a major problem of drinking water. There are several gases, microorganisms and other toxins (chemicals and heavy metals) added into water during rain, flowing water, etc. which is responsible for water pollution. This review article describes various applications of nanomaterial in removing different types of impurities from polluted water. There are various kinds of nanomaterials, which carried huge potential to treat polluted water (containing metal toxin substance, different organic and inorganic impurities) very effectively due to their unique properties like greater surface area, able to work at low concentration, etc. The nanostructured catalytic membranes, nanosorbents and nanophotocatalyst based approaches to remove pollutants from wastewater are eco-friendly and efficient, but they require more energy, more investment in order to purify the wastewater. There are many challenges and issues of wastewater treatment. Some precautions are also required to keep away from ecological and health issues. New modern equipment for wastewater treatment should be flexible, low cost and efficient for the commercialization purpose.

Preparation of CdS-TiO2-Based Palladium Heterogeneous Nanocatalyst by Solvothermal Route and Its Catalytic Activity for Reduction of Nitroaromatic Compounds

In this study, bare CdS nanoparticles (NPs) were prepared by solvothermal method using CdCl₂(3-methylbenzaldehyde thiosemicarbazone)₂ as a single-source molecular precursor in the presence of ethylene glycol. Further, these CdS NPs were used for the preparation of binary (CdS-TiO₂) and ternary (CdS-TiO₂/Pd) heterogeneous nanocatalysts. Characterization of the as-prepared nanocatalysts has been carried out using different techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy, and photoluminescence studies. The peak observed at 2θ = 39.5° in XRD confirms the successful doping of noble metal (Pd) on the surface of CdS-TiO₂ nanocatalyst, which is well supported by Raman analysis. From FESEM and TEM analyses, mixed morphology has been observed and elemental composition was confirmed by energy-dispersive X-ray spectroscopy elemental mapping. Furthermore, the as-prepared bare CdS NPs, binary CdS-TiO₂, and ternary CdS-TiO₂/Pd heterogeneous nanocatalysts were used for the reductive transformation of various nitroaromatic compounds to their corresponding aromatic amines at room temperature. It has been observed that among all of the catalysts, ternary CdS-TiO₂/Pd heterogeneous nanocatalyst has excellent catalytic property to reduce all nitroaromatic compounds in very short time span.

Effect of crystalline structure on terbuthylazine degradation by H2O2-assisted TiO2 photocatalysis under visible irradiation

Various methods for shifting the optical response of TiO₂ into the visible (Vis) range have been reported. Herein, we reported the application of a TiO₂/H₂O₂/Vis process and the effects of TiO₂ crystalline structure on the degradation of terbuthylazine. The results indicated that TiO₂ crystalline structure and H₂O₂ addition had significant effects on terbuthylazine degradation: its degradation rate could be increased from 7% to 70% with H₂O₂ addition after 180 min of reaction, the synergistic degradation of terbuthylazine by TiO₂-Fe³⁺ was substantially accelerated, with the degradation rate reaching up to 100% after 20 min of reaction, and rutile TiO₂ showed better photocatalytic activity and a more obvious synergistic effect than anatase TiO₂. The addition of free-radical scavengers (tert-butyl alcohol or methanol) inhibited the degradation efficiency of rutile TiO₂, but had a relatively minor effect on anatase TiO₂. Fluorescence spectrophotometry analysis indicated that hydroxyl free radicals could be continuously produced when using rutile TiO₂ as the photocatalyst. Degradation of terbuthylazine catalyzed by rutile TiO₂ occurred mainly in solution, but occurred on the particle surface of the photocatalyst when catalyzed by anatase TiO₂. This study provides new insight into the role of TiO₂ crystalline structure on the degradation of terbuthylazine and its photocatalytic degradation mechanism.

Application of thermal lens microscopy (TLM) for measurement of Cr(VI) traces in wastewater

In this work, we demonstrate for the first time that Thermal Lens Microscopy technique (TLM) can be applied to monitor the dynamics of a photocatalytic process in-situ. The photocatalytic reduction of hexavalent chromium -Cr(VI)- in aqueous solution using CdS and irradiated with visible light is monitored by TLM. Since the values of Cr(VI) concentration obtained after the photocatalytic process were close to those imposed by the international regulations for drinking water, the use of TLM allowed its measurement with a better reliability than with UV spectroscopy, usually used in this kind of analysis.

Recent Advances in the Use of Black TiO2 for Production of Hydrogen and Other Solar Fuels

Black TiO₂ has emerged as one of the most promising photocatalysts recently discovered. The reason behind its catalytic activity is considered to be due to the presence of defects and Ti³⁺ species at the surface of black TiO₂ nanostructures, which are crucial for its diverse applications. Moreover, disordered/crystalline surface layers and bulk regions have been identified and appear to influence the intrinsic properties of the material. Here, we present the latest studies on the use of black TiO₂ for metal free hydrogen production, as well as for CO₂ photoreduction and N₂ photofixation. After highlighting the structure/property relations, we conclude with some critical questions and suggest further topics of research in order to better understand the underlying mechanisms of light absorption in black TiO₂ , especially towards solar fuels production.

Photocatalytic Degradation of Tetracycline Hydrochloride via a CdS-TiO₂ Heterostructure Composite under Visible Light Irradiation

A photocatalytic active CdS-TiO₂ heterostructure composite was prepared by hydrothermal method and its morphology and properties were characterized. Results indicate that the CdS nanoparticles deposited on the surface of a TiO₂ nanoparticles, which was in anatase phase. The particle scale of both of the components reached approximately 15 nm. In comparison to pure TiO₂ (410 nm), the light absorption edge of the heterostructure composite was 550 nm, which could extend the light response from UV to the visible region. Under visible light irradiation, the degradation efficiency of tetracycline hydrochloride by the CdS-TiO₂ composite achieved 87.06%, significantly enhancing photocatalytic activity than the as-prepared pure TiO₂ and commercial TiO₂ (Degussa P25). This character is attributed to the synergetic effect of these two components in the absorption of visible light.

Highly-efficient photocatalytic degradation of methylene blue by PoPD-modified TiO 2 nanocomposites due to photosensitization-synergetic effect of TiO2 with PoPD

Poly-o-phenylenediamine modified TiO₂ nanocomposites were successfully synthesized via an ‘in situ’ oxidative polymerization method. The modified nanocomposites were characterized by BET, XRD, TEM, FT-IR, TGA, XPS, EA and UV-Vis DRS. The photocatalytic degradation of methylene blue was chosen as a model reaction to evaluate the photocatalytic activities of TiO₂ and PoPD/TiO₂. The results indicated that PoPD/TiO₂ nanocomposites exhibited good photocatalytic activity and stability. The photocatalytic activity of PoPD/TiO₂ increased as the initial pH increased because of electrostatic adsorption between the photocatalyst and MB as well as the generation of ·OH, whereas it exhibited an earlier increasing and later decreasing trend as the concentration of the photocatalyst increased owing to the absorption of visible light. The photocatalytic stability of the PoPD/TiO₂ nanocomposite was dependent on the stability of its structure. Based on radical trapping experiments and ESR measurements, the origin of oxidizing ability of PoPD/TiO₂ nanocomposites on photocatalytic degradation of MB was proposed, which taking into account of ·OH and ·O₂⁻ were the first and second important ROS, respectively. The possible photocatalytic mechanism and photocatalytic activity enhanced mechanism has been proposed, taking into account the photosensitization effect and synergetic effect of TiO₂ with PoPD.

Synthesis, properties, and applications of black titanium dioxide nanomaterials

Photocatalysis has been regarded as one of best solutions to using the sunlight to produce hydrogen from water and to removing organic pollutants from the environment, and titanium dioxide (TiO₂) nanomaterials have been treated as the primary photocatalyst for these purposes. However, their large band gap has largely limited the activity to the UV region of the solar spectrum. The discovery of black TiO₂ in 2011 has triggered world-wide research interests with new hope to overcome this problem. This review briefly summarizes the recent progresses of black TiO₂ nanomaterials, including their synthesis, properties and applications, to provide a timely update and to inspire more ideas in the related research.

Developing an efficient NiCo2S4 cocatalyst for improving the visible light H2 evolution performance of CdS nanoparticles

NiCo₂S₄ is developed as a noble-metal-free, efficient and stable cocatalyst for improving the visible light H₂ evolution performance of CdS nanoparticles.

Synthesis of porous ZnS, ZnO and ZnS/ZnO nanosheets and their photocatalytic properties

Porous ZnS, ZnO and ZnS–ZnO nanosheets (NSs) are obtained by annealing ZnS(en)_0.5 (en = ethylenediamine) NSs under suitable conditions in air.

Graphene in Photocatalysis: A Review

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H₂ production, and CO₂ reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

Quantum dot sensitized electrospun mesoporous titanium dioxide hollow nanofibers for photocatalytic applications

TiO₂ hollow nanofibers prepared by coaxial electrospinning were sensitized with CdS QDs by SILAR method and their photocatalytic dye degradation performance was investigated.

Hierarchical photocatalysts

The design, fabrication, performance and applications of hierarchical semiconductor photocatalysts are thoroughly reviewed and apprised.

Synergistic Effect of Dual Electron-Cocatalysts for Enhanced Photocatalytic Activity: rGO as Electron-Transfer Mediator and Fe(III) as Oxygen-Reduction Active Site

For a high-performance cocatalyst-modified photocatalyst, an effective interfacial separation of photogenerated electron from its corresponding holes and its following reduction reaction at the active sites are highly required. However, it is difficult for a single-component cocatalyst to simultaneously realize the crucial functions. In this study, an effective interfacial transfer of photogenerated electrons and its following rapid oxygen-reduction can be easily realized in a dual electron-cocatalyst modified Fe(III)/rGO-TiO₂ photocatalyst, where the rGO nanosheets function as an electron-transfer mediator for the effective transfer of photogenerated electrons from the TiO₂ surface while the Fe(III) cocatalyst serves as an electron-reduction active site to promote the following interfacial oxygen reduction. In this case, the rGO nanosheets were firstly loaded on the TiO₂ nanoparticle surface by a hydrothermal method and then the Fe(III) cocatalyst was further modified on the rGO nanosheets by an impregnation method to prepare the Fe(III)/rGO-TiO₂ photocatalyst. It was found that the dual electron-cocatalyst modified Fe(III)/rGO-TiO₂ photocatalyst showed an obviously higher photocatalytic performance than the naked TiO₂ and single-cocatalyst modified photocatalysts (such as Fe(III)/TiO₂ and rGO-TiO₂) owing to the synergistic effect of rGO and Fe(III) bi-cocatalysts. The present work can provide some new insights for the smart design of high-efficiency photocatalytic materials.

One-pot synthesis of a TiO2–CdS nano-heterostructure assembly with enhanced photocatalytic activity

An unprecedented morphology of a titanium dioxide (TiO₂) and cadmium sulfide (CdS) self-assembly obtained using a ‘truly’ one-pot and highly cost effective method with a multi-gram scale yield is reported here.

Amorphous Co3O4 modified CdS nanorods with enhanced visible-light photocatalytic H2-production activity

Amorphous Co₃O₄ modified CdS nanorods exhibit a significantly enhanced photocatalytic activity for H₂ production.

Facile synthesis and photocatalytic properties of ZnO core/ZnS–CdS solid solution shell nanorods grown vertically on reductive graphene oxide

The synthesis of ZnO core/Zn_xCd_1−xS shell nanorods grown vertically on RGO sheets and the important role played by Zn_xCd_1−xS on photocatalytic activity are described.