CdSe nanostructured thin film by electrophoretic deposition for quantum dots sensitized solar cell

Cadmium selenide (CdSe) quantum dots (QDs) with different size, 2.5 and 3.2 nm, were successfully deposited on mesoporous titanium dioxide (TiO2) (Degussa-P25) nanostructures by electrophoretic deposition method (EPD) at the applied voltage 100 V for 120 s deposition time. In this study, the morphology of CdSe films deposited by EPD and the performance of the film when assembled into a solar cell were investigated. From the field emission scanning electron microscopy cross-section, the thickness of the CdSe nanoparticles with size 2.5 nm films were 3.4 and 3.0μm for CdSe 3.2 nm nanoparticles film. The structure of 2.5 nm is denser than compare of 3.2 nm CdSe nanoparticles. From UV visible spectroscopy, the band gap calculated for 2.5 nm CdSe nanoparticles is 2.28 eV and for 3.2 nm is 2.12 eV. Photovoltaic characterization was performed under an illumination of 100 mW cm-2. A photovoltaic conversion efficiency of 1.81% was obtained for 2.5 nm CdSe and 2.1% was obtained for 3.2 nm CdSe nanoparticles. This result shows that the photovoltaic efficiency is dependent on CdSe nanoparticle size.

Towards a promising systematic approach to the synthesis of CZTS solar cells

This study aims to enhance the CZTS device's overall efficiency, the key research area has been identified in this study is to explore the effects of a novel, low-cost, and simplified, deposition method to improve the optoelectronic properties of the buffer layer in the fabrication of CZTS thin film solar cells. Herein, an effective way of addressing this challenge is through adjusting the absorbers' structure by the concept of doping, sensitized CdS thin film by the bi-functional linker, and an environmentally friendly catalytic green agent. The Linker Assisted and Chemical Bath Deposition (LA-CBD) method was introduced as an innovative and effective hybrid sensitization approach. In the one-step synthesis process, Salvia dye, Ag, and 3-Mercaptopropionic acid (MPA) were used. Generally, the results for all samples displayed varying bandgap as achieved between (2.21-2.46) eV, hexagonal structure with considerably decreased strain level, broader grain size, and dramatically enhanced crystalline property. Hence, the rudimentary CdS/CZTS solar cell devices were fabricated for the application of these novel CdS films. Preliminary CZTS thin film solar cell fabrication results in the highest conversion efficiency of 0.266% obtained CdS + Salvia dye, indicating the potential use of the CdS films as a buffer layer for CZTS photovoltaic devices.

Metal sulphides and their heterojunctions for photocatalytic degradation of organic dyes-A comprehensive review

Water pollution caused by organic dyes is one of the greatest threats to the ecosystem. The removal of dyes from water has remained a challenge for scientists. Recently, metal sulphides have emerged as a potential candidate for water remediation applications. The efficient charge transportation, greater surface-active sites, and low bandgap of metal sulphides make them an excellent choice of semiconductor photocatalysts for degradation of dyes. This review summarises the potential application of metal sulphides and their heterojunctions for the photocatalytic degradation of organic dyes from wastewater. A detailed study has been presented on the synthesis, basics of photodegradation and heterojunctions and photocatalytic activity. The effect of the use of templates, doping agents, synthesis route, and various other factors affecting the photocatalytic activity of metal sulphides have been summarised in this review. The synthesis techniques, characterisation techniques, mechanism of degradation of organic dyes by Z-scheme heterojunction photocatalyst, reusability and stability of metal sulphides, and the scope of future research are also discussed. This study indicates that Scopus-based core gathered data could be used to give an objective overview of the global dye degradation research from 2008 to 2023 (15 years). All data (articles, authors, keywords, and publications) is compiled in the Scopus database. For the bibliometric study, 1962 papers relevant to dye photodegradation by sulfide-based photocatalysts were found, and this number rises yearly. A bibliometric analysis provides a 15-year evaluation of the state-of-the-art research on the impact of metal sulfide-based photocatalysts on the photodegradation of dyes.

Direct Interfacial Excitation from TiO2 to Cu(II) Nanoclusters Enables Cathodic Photoresponse for Hydrogen Evolution under Visible-Light Irradiation

The titanium dioxide (TiO₂ ) photocatalyst is only active under UV irradiation due to its wide-gap nature. A novel excitation pathway denoted as interfacial charge transfer (IFCT) has been reported to activate copper(II) oxide nanoclusters-loaded TiO₂ powder (Cu(II)/TiO₂ ) under visible-light irradiation for only organic decomposition (downhill reaction) so far. Here, the photoelectrochemical study shows that the Cu(II)/TiO₂ electrode exhibits a cathodic photoresponse under visible-light and UV irradiation. It originates from H₂ evolution on the Cu(II)/TiO₂ electrode, while O₂ evolution takes place on the anodic side. Based on the concept of IFCT, a direct excitation of electrons from the valence band of TiO₂ to Cu(II) clusters initiates the reaction. This is the first demonstration of a direct interfacial excitation-induced cathodic photoresponse for water splitting without any addition of a sacrificial agent. This study is expected to contribute to the development of abundant visible-light-active photocathode materials for fuel production (uphill reaction).

Linker-Assisted CdS-TiO2 Nanohybrids as Reusable Visible Light Photocatalysts for the Oxidative Hydroxylation of Arylboronic Acids

A variety of phenols have been obtained in aqueous media with moderate to excellent chemical yields (≤100%) by using arylboronic acids and esters as substrates, a robust CdS-TiO₂ nanohybrid as a heterogeneous photocatalyst, visible light irradiation (467 nm), and an O₂-saturated atmosphere. The nanohybrid was prepared through a linker-assisted methodology that uses mercapto alkanoic acids as the organic linkers. The nanohybrid showed improved photocatalytic activity in the hydroxylation of substituted arylboronic acids and phenyl boronic esters compared with that of pristine CdS quantum dots. The nanohybrid can be reused in up to five photocatalytic cycles with ∼90% of its outstanding activity preserved.

A Z-scheme CdS/Ag3PO4 catalyst: Characterization, experimental design and mechanism consideration for methylene blue

Due to the explosive use of Azo dyes in various industries such as textiles, discharging these industrial effluents into the environment critically polluted water supplies. Accordingly, constructing/developing novel binary catalysts to diminish the pollution extent of such effluents before discharging into environment is an excellent issue in environmental chemistry. Here, a binary CdS/ Ag₃PO₄ was constructed, and its boosted photocatalytic activity was proven against methylene blue (MB), as a model dye pollutant. The Wurtzite CdS and Ag₃PO₄ cubic crystal nanoparticles were synthesized and coupled mechanically. The binary sample's lowest photoluminescence (PL) results confirm a higher e/h separation. DRS results confirmed a decreased energy gap for the coupled system. The semiconductors' VB and CV potentials were calculated and used for constructing of Z-scheme mechanism. The photocatalytic activity was followed via an experimental design approach. The model F-value of 89.75 > F_0.05,14,13 = 2.42 and LOF F-value of 6.57 < F_{0.05,10, 3} = 8.79 reveal that the model well processed data. The optimal run conditions were CMB: 5 ppm, Catalyst dose: 1 g/L, pH: 3.25, and irradiation time: 139 min, at which 85% of MB molecules were degraded. Based on the trend of ascorbic acid > isopropanol > formic acid ≈ nitrate obtained for the scavengers' importance in decreasing the photocatalyst activity, superoxide radicals had the highest effect in MB degradation and then ^•OH. The results showed the direct Z-scheme has the main effect on MB degradation by the binary sample.

Biomimetic nitrogen-rich photocatalyst based on cadmium sulfide for photocatalytic hydrogen evolution

A novel N-rich sugarcane-like photocatalyst CdS/C₃N₅ (CCN) was prepared by a thermal polymerization method and tested for generating H₂ and realizing antiphotocorrosive performance. The best photocatalytic H₂ evolution is obtained for a CdS to C₃N₅ mass ratio of 1:1 (CCN3), which is nearly 33 and 3 times higher than that of pure C₃N₅ and CdS, respectively. CCN3 can be used to effectively reduce CdS photocorrosion and increase stability because of its N-rich performance and sugarcane-like structure, which can affect electron transport and enhance the internal binding force, respectively. CCN3 can maintain a high H₂ evolution ability after 5 cycles, while still maintaining the original sugarcane-like shape, which has an anti-photocorrosive ability.

MOF-derived sulfur vacancies rich CdS nanoparticles in situ growth on 2D polymer for highly efficient photocatalytic hydrogen generation

For heterojunction photocatalytic materials, the size of nanoparticles and electron-hole separation efficiency have a great influence on the photocatalytic hydrogen production activity. In this work, for the first time, a...

Roles of Mo dopant in Bi2WO6 for enhancing photocatalytic activities

We present the investigation of the roles of molybdenum (Mo) dopant with a concentration of 0.0625% to 1.0% Mo into bismuth tungstate (Bi₂WO₆) by a one-step hydrothermal method for the enhancement of photocatalytic activities. The obtained materials and doping effects were characterized by the morphology, crystal structure, chemical states, and optical properties. By combining XRD, XANES, and EXAFS studies, the distortion of the local structure with substitutional doping was revealed as doping with Mo ions was located at the lattice sites of the tungsten ions. Photocatalytic reactions of Mo-doped Bi₂WO₆ were studied by the degradation of methyl orange dye under visible light irradiation. The results show that the optimal concentration of Mo dopant is 0.25%, with the highest photocatalytic activity up to ∼2-fold compared to the bare Bi₂WO₆. From our investigation, we propose that the impurity level is located below the conduction band edge of Bi₂WO₆ after doping with Mo⁶⁺ ions. This impurity level acts as an electron trapping site to prevent the transition of excited electrons from the conduction band to the valence band. By trapping experiments, the superoxide anion radicals (O₂˙^-) as the main active species to enhance photocatalytic efficiency was established.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

Elucidating the Factors Affecting Hydrogen Production Activity Using a CdS/TiO2 Type-II Composite Photocatalyst

CdS/TiO2 is a composite photocatalyst that has been studied over many years and in which electron transfer from CdS to TiO2 is believed to lead to high photocatalytic activity. However, most reports on improved activity involve hydrogen production in the presence of a sulfide reducing agent. In this study, we comprehensively examined the effects of electron transfer, hydrogen overvoltage, substrate adsorption, and the cocatalyst from relationships between hydrogen production ability and the total number of trapped electrons in the presence of various reducing agents. As a result, we clarified that the electron transfer between CdS and TiO2 does not necessarily lead to high activity. We showed that the composite photocatalyst needs to be designed for the intended purpose and that evaluating the hydrogen production ability using sacrificial reagents provides insufficient information for use in an actual environment.

Tailored Coupling of Biomineralized CdS Quantum Dots to rGO to Realize Ambient Aqueous Synthesis of a High-Performance Hydrogen Evolution Photocatalyst

Nanocomposite photocatalysts offer a promising route to efficient and clean hydrogen production. However, the multistep, high-temperature, solvent-based syntheses typically utilized to prepare these photocatalysts can limit their scalability and sustainability. Biosynthetic routes to produce functional nanomaterials occur at room temperature and in aqueous conditions, but typically do not produce high-performance materials. We have developed a method to produce a highly efficient hydrogen evolution photocatalyst consisting of CdS quantum dots (QDs) supported on reduced graphene oxide (rGO) via enzyme-based syntheses combined with tuned ligand exchange-mediated self-assembly. All preparation steps are carried out in an aqueous environment at ambient temperature. Size-controlled CdS QDs and rGO are prepared through enzyme-mediated turnover of l-cysteine to HS^- in aqueous solutions of Cd-acetate and graphene oxide, respectively. Exchange of cysteamine for the native l-cysteine ligand capping the CdS QDs drives self-assembly of the now positively charged cysteamine-capped CdS (CdS/CA) onto negatively charged rGO. The use of this short linker molecule additionally enables efficient charge transfer from CdS to rGO, increasing exciton lifetime and, subsequently, photocatalytic activity. The visible-light hydrogen evolution rate of the resulting CdS/CA/rGO photocatalyst is 3300 μmol h^-1 g^-1. This represents, to our knowledge, one of the highest reported rates for a CdS/rGO nanocomposite photocatalyst, irrespective of the synthesis method.

Physical Origin of Diminishing Photocatalytic Efficiency for Recycled TiO2 Nanotubes and Ag-Loaded TiO2 Nanotubes in Organic Aqueous Solution

Arrays of titania nanotubes (TiO2NTs) were developed by electrochemical anodization and doped with silver on their surface by photodeposition to achieve TiO2NTs/Ag. It is found that only anatase TiO2NTs were formed, with the preferential growth direction perpendicular to the titanium substrate, and with the length and diameter of ~2 µm and 90–120 nm, respectively. The presence of Ag on the surface of TiO2NTs was also confirmed. The TiO2NTs and TiO2NTs/Ag were used as photocatalysts to decolorize the methylene blue (MB) aqueous solution. The photodegradation efficiency (PDE) is as high as 83% for TiO2NTs and 98% for TiO2NTs/Ag photocatalysts. This work focused on the investigation of the stability and recyclability of these photocatalysts in terms of efficiency and its physical origin by surface analysis using X-ray photoelectron spectroscopy (XPS). It is found that PDE diminishes from 83% to 76% in TiO2NTs upon eight recycling runs and from 98% to 80% in TiO2NTs/Ag upon six recycling runs. The XPS analysis revealed that the physical origin of diminishing efficiency is the carbon contamination on the surface of recycled TiO2NTs and a combination of carbon contamination and Ag leaching in recycled TiO2NTs/Ag.

The Effects of NaI, KBr, and KI Salts on the Vapor-Liquid Equilibrium of the H2O+CH3OH System

The vapor–liquid equilibrium (VLE) in chemical engineering is indispensable for the design of equilibrium separation processes such as distillation, absorption, extraction, and crystallization. VLE data were measured for H₂O+CH₃OH+NaI, H₂O+CH₃OH+KBr, and H₂O+CH₃OH+KI systems. By analyzing and summarizing the results of H₂O+Methanol+Alkali metal halide systems, the salt effects of NaI, KBr, and KI on the vapor–liquid equilibrium were obtained. Simultaneously, a model based on the NRTL equation (non-random two liquid) was proposed to correlate and calculate the VLE for the systems. In addition, the assumption of solvation based on hydration was introduced in this model. The proposed model can be successfully used to calculate the VLE for H₂O+Methanol+Alkali metal halide systems.

Dual responsive magnetic Fe3O4-TiO2/graphene nanocomposite as an artificial nanozyme for the colorimetric detection and photodegradation of pesticide in an aqueous medium

The Fe₃O₄-TiO₂/reduced graphene oxide (Fe₃O₄-TiO₂/rGO) nanocomposite was successfully prepared by one step hydrothermal method and exhibit intrinsic peroxidase mimic activity and photocatalytic efficiency. The as-prepared nanomaterials were characterized by several analytical tools including XRD, HRTEM, FESEM, XPS, VSM, FT-IR, AFM, TGA and zeta potential analysis. The average particle size of Fe₃O₄ and TiO₂ NPs on the rGO nanosheets are found to be 9 ± 0.2 nm. The synthesized nanocomposite showed dual responsive including highly sensitive colorimetric detection of harmful atrazine pesticide in an aqueous medium as well as photocatalytic degradation of atrazine pesticide. The Fe₃O₄-TiO₂/rGO nanocomposite showed the efficient peroxidase-like catalytic activity throughout the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) as a peroxidase substrate to the blue-colored oxidized product (ox-TMB) in presence of H₂O₂. Based on this observation, the colorimetric detection technique is applied for the sensing of atrazine as model pesticides using TMB as a peroxidase substrate molecule and 2.98 μg/L of the limit of detection (LOD) was obtained in the linear range of 2-20 μg/L. Thus the proposed colorimetric sensing technique is simple and low cost for the real-time monitoring of the pesticides in an aqueous medium. Further, the Fe₃O₄-TiO₂/rGO nanocomposite was also successfully utilized towards efficient photocatalytic degradation of atrazine molecule (100 %) under irradiation of natural sunlight. Moreover, Fe₃O₄-TiO₂/rGO nanocomposite was successfully recycled for 10 times without a significant loss of its photocatalytic efficiency. This work delivers a new insight for the dual responsive of the Fe₃O₄-TiO₂/rGO nanocomposite as an artificial nanozyme for colorimetric sensing of the water pollutant and also removal of the water pollutant by simple photocatalytic degradation method under natural sunlight irradiation.

Preparation and Photocatalytic Properties of CdS/F–TiO2 Composites

F–TiO2 was prepared by a simple precipitation method using titanium sulfate as the titanium source, hydrogen fluoride as the fluorine source and ammonia as the precipitant. CdS/F–TiO2 composites were prepared by hydrothermal synthesis of CdS and F–TiO2. The surface morphology, crystal phase composition, ultraviolet absorption band, fluorescence intensity, element composition, valence state, specific surface and pore structure of the samples were characterized by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet visible absorption spectrum (UV-Vis-Abs), Molecular fluorescence spectrophotometer (PL) and X-Ray photoelectron spectroscopy (XPS) and Surface area analyzer (BET), respectively. The effects of the dosage of the photocatalyst, pH value, the concentration of methyl orange and the addition of H2O2 on the photocatalytic performance were investigated with methyl orange solution as the target degradation product. The results showed the optimum condition for photodegradation of methyl orange by 1% CdS/F–TiO2 is that the pH value, the solid-liquid ratio, the concentration of methyl orange and the dosage of H2O2 is 2, 2 g/L, 10 mg/L and 3%, respectively. Under the same conditions, the degradation rate of methyl orange by 1% CdS/F–TiO2 was 93.36% when 300 W metal halide lamp was irradiated for 20 minutes, which was significantly higher than that of F–TiO2. CdS has a significant effect on the morphology, crystallinity, grain size and the compound probability of electrons and holes after the F–TiO2 modification. The composite causes a significant red shift at the edge of the F–TiO2 light absorption band. The photocatalytic degradation of methyl orange by 1% CdS/F–TiO2 follows the Langmuir-Hinshelwood first-order kinetic model.

Attaching titania clusters of various size to reduced graphene oxide and its impact on the conceivable photocatalytic behavior of the junctions-a DFT/D + U and TD DFTB modeling

DFT/D  +  U and density functional based tight binding (DFTB) molecular modeling was used to investigate the role of the structural, electronic and optical properties of reduced graphene oxide surface (r-GO), hybridized with hydrated TiO₂ moieties of various size, ranging from small molecular Ti₂O₄ clusters into extended Ti₄₃O₈₆ rutile type nanocrystals of ~5 nm diameter. The calculated adhesion energies, varying from  -5.048 eV (r-GO|Ti₂O₄), -12.159 eV (r-GO|Ti₅O₁₀), -18.499 eV (r-GO|Ti₁₅O₃₀) to  -42.484 eV (r-GO|Ti₄₃O₈₆), indicate high stability of these composites. It was shown that electronic interactions at the r-GO|(1 1 0)TiO₂ interface give rise to net charge flow from the r-GO substrate towards the TiO₂ moieties, analyzed in terms of the partial charge density 3D plots and an interfacial dipole moment formation. The DOS structure of the composites was calculated by means of the time dependent DFTB approach, and the position and composition of the VB and CB edges, along with the presence of weak mid-gap 2p  C states originating from the intact graphene-like patches in the r-GO substrate were discussed in detail in the context of conceivable photocatalytic activity of the composites. The constructed band alignment diagram implies formation of the staggered type II scheme, with the electric field offset that is sensitive to the titania cluster size. In the case of the nano-reticular TiO₂, where only a fraction of the Ti atoms is engaged in the Ti-O-C linkers formation, recombination of the photogenerated charges is inhibited owing to favorable spatial separation effect. For small molecular TiO₂ clusters with all Ti cations anchored to the r-GO layer fast cross-relaxation quenches the beneficial interfacial charge separation effect, since the strong hybridization of the oxygen and carbon states provides a convenient pathway for the efficient electronic coupling between the CB edge states of r-GO and the VB edge states of the TiO₂ moieties. A phenomenological model of the molecular r-GO|Ti₂O₄ and the reticular r-GO|Ti₄₃O₈₆ composites was constructed in account for different photocatalytic behavior of both junctions.

Surface-enhanced Raman scattering (SERS) as a probe for detection of charge-transfer between TiO2 and CdS nanoparticles

The differences of charge transfer processes in different assemblies were observed by the optical method of SERS.

CO2-based hydrogen storage – hydrogen liberation from methanol/water mixtures and from anhydrous methanol

New strategies for the reforming of methanol under mild conditions on the basis of heterogeneous and molecular catalysts have raised the hopes and expectations on this fuel. This contribution will focus on the progress achieved in the production of hydrogen from aqueous and anhydrous methanol with molecular and heterogeneous catalysts. The report entails thermal approaches, as well as light-triggered dehydrogenation reactions. A comparison of the efficiency and mechanistic aspects will be made and principles of catalytic pathways operating in biological systems will be also addressed.

Quantum dot-decorated semiconductor micro- and nanoparticles: A review of their synthesis, characterization and application in photocatalysis

Quantum dot (QD)-decorated semiconductor micro- and nanoparticles are a new class of functional nanomaterials that have attracted considerable interest for their unique structural, optical and electronic properties that result from the large surface-to-volume ratio and the quantum confinement effect. In addition, because of QDs' excellent light-harvesting capacity, unique photoinduced electron transfer, and up-conversion behaviour, semiconductor nanoparticles decorated with quantum dots have been used widely in photocatalytic applications for the degradation of organic pollutants in both the gas and aqueous phases. This review is a comprehensive overview of the recent progress in synthesis methods for quantum dots and quantum dot-decorated semiconductor composites with an emphasis on their composition, morphology and optical behaviour. Furthermore, various approaches used for the preparation of QD-based composites are discussed in detail with respect to visible and UV light-induced photoactivity. Finally, an outlook on future development is proposed with the goal of overcoming challenges and stimulating further research into this promising field.

Preparation of CdS and Bi2S3 quantum dots co-decorated perovskite-type KNbO3 ternary heterostructure with improved visible light photocatalytic activity and stability for phenol degradation

A combination of the hydrothermal route with a linker assisted attachment method was used to obtain efficient CdS/Bi₂S₃ quantum dot-decorated perovskite type KNbO₃.

One-pot hydrothermal synthesis of CdS decorated CuS microflower-like structures for enhanced photocatalytic properties

CdS decorated CuS structures have been controllably synthesized through a one-pot hydrothermal method. The morphologies and compositions of the as-prepared samples could be concurrently well controlled by simply tuning the amount of CdCl2 and thiourea. Using this strategy, the morphology of the products experienced from messy to flower-like morphologies with multiple porous densities, together with the phase evolution from pure CuS to the CdS/CuS composites. Serving as a photocatalyst, the samples synthesized with the addition of 1 mmol cadmium chloride and 3 mmol thiourea during synthetic process, showed the best photocatalytic activity, which could reach a maximum photocatalytic efficiency of 93% for methyl orange (MO) photodegradation after 150 min. The possible mechanism for the high photocatalytic efficiency of the sample was proposed by investigating the composition, surface area, structure, and morphology before and after photocatalytic reaction.

Application of ultrasound-aided method for the synthesis of CdS-incorporated three-dimensional TiO2 photocatalysts with enhanced performance

In this study, an ultrasound-aided hydrothermal-impregnation method was used to synthesize three-dimensional (3D) urchin-like CdS-TiO₂ nanostructures (UCTs) with variable CdS content. The photocatalytic efficiencies (for degrading limonene and toluene vapor) of UCTs synthesized using the ultrasound-aided process were greater than those of UCTs fabricated without ultrasound treatment. In addition, the photocatalytic efficiencies of ultrasound-treated UCTs were greater than those of zero-dimensional ultrasound-treated CdS-TiO₂ particles, which, in turn, were greater than those of untreated 3D TiO₂. These results indicate that ultrasonication is an amicable process for the synthesis of UCTs with high photocatalytic activity. The enhanced activity of ultrasound-treated photocatalysts is ascribed to the greater charge carrier efficiency, adsorption capacity, and light absorption efficiency of these materials. The photocatalytic efficiencies of ultrasound-treated UCTs increased as the CdS loading was increased from 0.1% to 0.3%, gradually dropping as the loading was further increased to 3.0%, which indicated the existence of an optimum CdS loading. UCT photocatalytic efficiencies depended on the input concentration of target pollutants, relative humidity, and air flow rate. The photocatalytic efficiency for the decomposition of limonene mixed with 2-propanol was lower than that for limonene alone, likely due to the radical scavenging properties of 2-propanol. However, the photocatalytic degradation efficiency of the latter alcohol was not changed upon admixture. Toluene exhibited the same behavior. The mineralization ratios of both target compounds were lower than their decomposition ratios, indicating formation of byproducts due to incomplete oxidation. In addition to CO, three organic compounds were observed as photocatalytic decomposition byproducts of limonene (acetic acid, limonene oxide, and methacrolein) and toluene (benzene, benzaldehyde, and p-xylene). UCTs synthesized by the ultrasound-aided hydrothermal-impregnation method could be used to decompose organic vapors with an efficiency of up to 98%, depending on operating conditions.

SERS as a probe for the charge-transfer process in a coupled semiconductor nanoparticle system TiO2/MBA/PbS

The TiO₂/MBA/PbS bi-semiconductor system is explored as a model to study the charge transfer process with SERS for the first time.

High-efficiency sono-solar-induced degradation of organic dye by the piezophototronic/photocatalytic coupling effect of FeS/ZnO nanoarrays

Highly-efficient sono-solar-induced degradation of organic dye by the piezophototronic/photocatalytic coupling effect of FeS/ZnO nanoarrays was achieved. A steel screen was used as the substrate for supporting FeS/ZnO nanoarrays, and the nanoarrays were vertically and uniformly grown on the substrate via a wet-chemical route. Under ultrasonic and solar irradiation, FeS/ZnO nanoarrays have high sono-photocatalytic activity for degrading methylene blue in water. The photogenerated carriers can be separated by a piezoelectric field and a built-in electric field, resulting in a low recombination rate and high photocatalytic efficiency. The piezophototronic and photocatalytic effects were coupled together. The experimental/theoretical data indicate that this novel wastewater treatment can co-use mechanical and solar energy in nature, and so is a promising technology for environment improvement.

Shape-Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers

1D mesoporous materials have attracted extensive interest recently, owning to their fascinating properties and versatile applications. However, it remains as a grand challenge to develop a simple and efficient technique to produce oxide nanofibers with mesoporous architectures, controlled morphologies, large surface areas, and optimal performances. In this work, a facile foaming-assisted electrospinning strategy with foaming agent of tea saponin is used to produce thoroughly mesoporous ZnO nanofibers with high purity and controlled morphology. Interestingly, mesoporous fibers with elliptical cross-section exhibit the significantly enhanced photocatalytic activity for hydrogen production, as compared to the counterparts with circular and rectangular cross-sections, and they also perform better than the commercial ZnO nanopowders. The unexpected shape dependence of photocatalytic activities is attributed to the different stacking modes of the mesoporous fibers, and a geometrical model is developed to account for the shape dependence. This work represents an important step toward producing thoroughly mesoporous ZnO nanofibers with tailored morphologies, and the discovery that fibers with elliptical cross-section render the best performance provides a valuable guideline for improving the photocatalytic performance of such mesoporous nanomaterials.

Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2 nanotubes for photocatalytic hydrogen generation

Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after ∼100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS measurements combined with optical band gap measurements. This property facilitates an improvement of the visible-light hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmol cm(-2) h(-1) for TiO2 nanotubes sensitized with CdS quantum dots.

Core-Shell Vanadium Modified Titania@β-In2S3 Hybrid Nanorod Arrays for Superior Interface Stability and Photochemical Activity

Core-shell rutile TiO2@β-In2S3 and modified V-TiO2@β-In2S3 were synthesized to develop bilayer systems to uphold charge transport via an effective and stable interface. Morphological studies revealed that β-In2S3 was deposited homogeneously on V-TiO2 as compared to unmodified TiO2 nanorod arrays. X-ray photoelectron spectroscopy (XPS) and electron energy loss spectrometry studies verified the presence of various oxidation states of vanadium in rutile TiO2 and the vanadium surface was utilized for broadening the charge collection centers in host substrate layer and hole quencher window. Subsequently, X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectra confirmed the rutile phases of TiO2 and modified V-TiO2 along with the phases of crystalline β-In2S3. XPS valence band study explored the interaction of valence band quazi Fermi levels of β-In2S3 with the conduction band quazi Fermi levels of modified V-TiO2 for enhanced charge collection at the interface. Photoelectrochemical studies show that the photocurrent density of V-TiO2@β-In2S3 is 1.42 mA/cm(2) (1.5AM illumination). Also, the frequency window for TiO2 was broadened by the vanadium modification in rutile TiO2 nanorod arrays, and the lifetime of the charge carrier and stability of the interface in V-TiO2@β-In2S3 were enhanced compared to the unmodified TiO2@β-In2S3. These findings highlight the significance of modifications in host substrates and interfaces, which have profound implications on interphase stability, photocatalysis and solar-fuel-based devices.

One-step solvothermal synthesis of carbon doped TiO2–MoS2 heterostructure composites with improved visible light catalytic activity

TiO₂–MoS₂ composites are prepared from a novel molybdenum–sulphur cluster, (NH₄)₂Mo₃S₁₃·2H₂O, and TiOP. A composite with 0.7% loaded MoS₂ showed enhanced visible light photodegradation properties.

Rational design of semiconductor-based photocatalysts for advanced photocatalytic hydrogen production: the case of cadmium chalcogenides

This review summarizes the recent advances in developing CdX (X = S, Se, Te)-based photocatalyst systems for photocatalytic hydrogen production from water.

Well-Dispersed and Size-Controlled Supported Metal Oxide Nanoparticles Derived from MOF Composites and Further Application in Catalysis

Supported metal oxide nanoparticles are important in heterogeneous catalysis; however, the ability to tailor their size, structure, and dispersion remains a challenge. A strategy to achieve well-dispersed and size-controlled supported metal oxides through the manageable growth of a metal organic framework (Cu-BTC) on TiO2 followed by pyrolysis is described.

Enhanced photoelectrochemical and photocatalytic activity of WO3-surface modified TiO2 thin film

Development of nanostructured photocatalysts for harnessing solar energy in energy-efficient and environmentally benign way remains an important area of research. Pure and WO3-surface modified thin films of TiO2 were prepared by magnetron sputtering on indium tin oxide glass, and photoelectrochemical and photocatalytic activities of these films were studied. TiO2 particles were <50 nm, while deposited WO3 particles were <20 nm in size. An enhancement in the photocurrent was observed when the TiO2 surface was modified WO3 nanoparticles. Effect of potential, WO3 amount, and radiations of different wavelengths on the photoelectrochemical activity of TiO2 electrodes was investigated. Photocatalytic activity of TiO2 and WO3-modified TiO2 for the decolorization of methyl orange was tested. Graphical abstractWO3-surface modified TiO2 film showing better photocatalytic and photoelectrocatalytic activity.