Shape-Dependent Photocatalytic Activity of Hydrothermally Synthesized Cadmium Sulfide Nanostructures

Designing Nanoengineered Photocatalysts for Hydrogen Generation by Water Splitting and Conversion of Carbon Dioxide to Clean Fuels

Semiconductor photocatalysis has received tremendous attention in the past decade as it has shown great promise in the context of clean energy harvesting for environmental remediation. Sunlight is an inexhaustible source of energy available to us throughout the year, although it is rather dilutely dispersed. Semiconductor based photocatalysis presents one of the best ways to harness this source of energy to carry out chemical reactions of interest that require external energy input. Photocatalytic hydrogen generation by splitting of water, CO₂ mitigation, and CO₂ conversion to green fuel have therefore become the highly desirable clean and sustainable processes for a better tomorrow. Although numerous efforts have been made and continue to be expended to search and develop new classes of photocatalyst materials in recent years, several significant challenges still remain to be resolved before photocatalysis can reach its commercial potential. Therefore, major attention is required towards improving the efficiencies of the existing photocatalysts by further manipulating them and parallelly employing newer strategies for novel photocatalyst designs. This personal account aims to provide a broad overview of the field primarily invoking examples of our own research contributions in the field, which include photocatalytic hydrogen generation and CO₂ reduction to value added chemicals. This account reviews the state-of-the-art research activities and scientific possibilities which a functional material can offer if its properties are put to best use through goal-oriented design by combining with other compatible materials. We have addressed fundamental principles of photocatalysis, different kind of functional photocatalysts, critical issues associated with them and various strategies to overcome the related hurdles. It is our hope that this current personal account will provide a platform for young researchers to address the bottleneck issues in the field of photocatalysis and photocatalysts with a sense of clarity, and to find innovative solutions to resolve them by a prudent choice of materials, synthesis protocols, and approaches to boost the photocatalysis output. We emphasize that a targeted or goal-directed photocatalyst nanoengineering as perhaps the only way to realize an early success in this multiparametric domain.

Strategies to Enhance ZnO Photocatalyst's Performance for Water Treatment: A Comprehensive Review

Despite the photocatalytic organic pollutant degradation using ZnO started in 1910-1911, many challenges are still ahead, and several critical issues have to be addressed. Large band gap, and short life-time of photogenerated electrons and holes are critical issues negatively affect the photocatalytic activity of ZnO. Various approaches have been introduced to overcome these issues including intrinsic doping, extrinsic doping, and heterostructure. This review introduces unique and deep insights into tuning of the photocatalytic activity of ZnO. It starts by description of how to tune the photocatalytic activity of pristine ZnO through tuning its morphology, surface area, exposed face, and intrinsic defects. Afterward, the review explains how the Z-scheme approach succeed to address the redox weakened issue of heterojunction approach. In general, this review provides a clear image that helps the researcher to tune the photocatalytic activity of pristine ZnO and its heterostructure.

Fabrication of S-scheme CdS-g-C3N4-graphene aerogel heterojunction for enhanced visible light driven photocatalysis

Constructing S-scheme heterojunction photocatalysts reveals a greatly improved separation efficiency of photogenerated carriers and enhanced harvesting ability of solar energy in photocatalytic field. Herein, a ternary CdS-g-C₃N₄-GA heterojunction has been fabricated by a facile ultrasound strategy, which behaved as a S-scheme heterojunction with an intimate interface formed, and GA played as an electronic transportation platform to promote the separation of photo-induced charge carriers, which was certified through photoelectrochemical techniques. Density functional theory calculations revealed that the different component in ternary CdS-g-C₃N₄-GA heterojunction demonstrated an obvious difference of work function, resulting in the charge transfer from CdS to g-C₃N₄ through GA with S-scheme principle. In the optimized conditions, the S-scheme CdS-g-C₃N₄-GA heterojunction not only displayed greatly enhanced photocatalytic performances for degradation of dye and antibiotic wastewater, but also improved photocatalytic H₂ production activity. In addition, the photocatalytic mechanism and driving force of charge transfer and separation in S-scheme CdS-g-C₃N₄-GA heterojunction were studied. This study offers a feasible strategy to construct a ternary S-scheme heterojunction for environmental and energy photocatalysis.

In situ growth of CuS NPs on 3D porous cellulose macrospheres as recyclable biocatalysts for organic dye degradation

Aiming at recyclable catalyst carriers, porous cellulose macrospheres from wood pulp dissolved in an alkaline urea system were regenerated by simple injection regeneration. After solvent exchange, porous cellulose macrospheres (CMs) with a high specific surface area of 325.3 m² g⁻¹ were obtained by lyophilization, and CuS nanoparticles (CuS NPs) were coated on CMs by in situ growth in the liquid phase to achieve CuS-supported CM macrospheres (CuS@CM). The results indicated that the CuS@CM biocatalyst was successfully prepared with an average diameter of approximately 1.2 mm. In addition, CuS@CM was further used as a heterogeneous catalyst for the catalytic degradation of methylene blue (MB) and methyl orange (MO) model dyes during the oxidation of hydrogen peroxide (H₂O₂). In the presence of low doses of H₂O₂, the degradation rate of MB reached 94.8% within 10 min, showing high catalytic activity under neutral and alkaline conditions. After five cycles, 90.1% of the original catalytic activity was still retained, indicating that the prepared CuS@CM composite possessed excellent catalytic activity and reusability.

CuS nanoparticles were grown in situ on 3D porous cellulose macrospheres for an excellent rapid cycling removal of organic dyes.

Tuning the morphology of CeO2 nanostructures using a template-free solvothermal process and their oxygen reduction reaction activity

In fuel cells, the oxygen reduction reaction (ORR) at the cathode plays a crucial role in their performance. High cost, low abundance, catalyst poisoning, and poor durability of the pioneering ORR catalyst Pt make it less desirable for commercial fuel cells. Herein, we demonstrate a greener process to synthesize CeO2 nanostructures by varying reaction parameters in a single-step solvothermal route and provide a detailed mechanism for the formation of CeO2 nanostructures with different shapes. The shape and size of the CeO2 nanostructures such as hollow/solid spheres, triangular flakes, nanotubes, and flower-like structures result in a strong effect on their ORR activity. A normalized effect of effective surface area and oxygen vacancies in CeO2 nanostructures is found to govern the ORR activity order. Among the CeO2 nanostructures, hollow spheres exhibit the best ORR activity with a four-electron reduction pathway. Moreover, they show comparable ORR activity and outstanding stability as well as methanol fuel tolerance and are a substitute for Pt/C.

Photosensitive Thin Films Based on Drop Cast and Langmuir-Blodgett Hydrophilic and Hydrophobic CdS Nanoparticles

Comparative photoelectrochemical studies of cadmium sulfide (CdS) nanoparticles with either hydrophilic or hydrophobic surface properties are presented. Oleylamine organic shells provided CdS nanoparticles with hydrophobic behavior, affecting the photoelectrochemical properties of such nanostructured semiconductor. Hydrophilic CdS nanoparticles were drop-cast on the electrode, whereas the hydrophobic ones were transferred in a controlled manner with Langmuir-Blodgett technique. The substantial hindrance of photopotential and photocurrent was observed for L-B CdS films as compared to the hydrophilic, uncoated nanoparticles that were drop-cast directly on the electrode surface. The electron lifetime in both hydrophilic and hydrophobic nanocrystalline CdS was determined, revealing longer carrier lifetime for oleylamine coated CdS nanoparticles, ascribed to the trapping of charge at the interface of the organic shell/CdS nanoparticle and to the dominant influence of the resistance of the organic shell against the flux of charges. The “on” transients of the photocurrent responses, observed only for the oleylamine-coated nanoparticles, were resolved, yielding the potential-dependent rate constants of the redox processes occurring at the interface.

Tetracycline Photocatalytic Degradation under CdS Treatment

Industrialization and the growing consumption of medicines leads to global aquatic contamination. One of the antibiotics widely used against bacterial infections in both human and veterinary medicine is tetracycline. Despite its positive antibiotic action, tetracycline is resistant against degradation, and therefore it accumulates in the environment, including the aquatic environment, creating great health hazards, possibly stimulating antibiotic resistance of pathogenic organisms. In this research, aqueous suspensions of semiconductor nanoparticles CdS were used for photocatalytic activity studies in the presence of methylene blue as a model compound, and finally, in the presence of tetracycline, a broad-spectrum antibiotic widely used against bacterial infections, as well as a live-stock food additive. The mechanism and kinetic rate constants of photocatalytic degradation processes of methylene blue and tetracycline were described in correlation with the energy diagram of CdS nanoparticles.

Engineering the Morphology and Crystal Phase of 3 D Hierarchical TiO2 with Excellent Photochemical and Photoelectrochemical Solar Water Splitting

Owing to their unique characteristics, hierarchical TiO₂ nanostructures have several advantages in solar-fuel production. In this work, a single-step approach has been developed to control both the crystal phase and morphology of TiO₂ with 3 D urchin-like structure via a surfactant-free solvothermal route. The growth of 3 D hierarchical structure with phase-engineered band alignment, the role of the H₂ O/HCl ratio, and fine-tuning of the reaction parameters are investigated systematically. An optimum ratio of anatase (41 %) to rutile (59 %) in the mixed-phase TiO₂ (AR-2) results in excellent photocatalytic H₂ generation activity of 5753 μmol g^-1 after 5 h of irradiation with apparent quantum yields of 20.9 % at 366 nm and 4.5 % at 420 nm. The superior performance of AR-2, attributed to efficient separation of charge carriers through the phase junction, is apparent from the transient photocurrent response and photoluminescence studies. The 3 D urchin-like pure rutile TiO₂ (R-1) composed of nanorods shows enhanced photocatalytic activity compared with pure anatase and pure rutile TiO₂ nanoparticles, and this demonstrates the role of morphology. The best-performing mixed-phase 3 D TiO₂ shows excellent durability up to 25 h and is shown to produce 3522 μmol g^-1 of H₂ under natural sunlight, which highlights its potential for long-term application.

Selectively Photocatalytic Activity of an Open-Framework Chalcogenide Built from Corner-Sharing T4 Supertetrahedral Clusters

The photocatalysis process with high selectivity is a very important research forefront for the semiconductor photocatalytic decomposition of organic pollutants. However, the rational design of efficient photocatalysts with high selectivity is still a challenge. Here, we present an open-framework chalcogenide (Heta)₈[In₁₄Sn₂Zn₄Se₃₃] (Heta = ethanolamine-H⁺) (compound 1) constructed from T4 supertetrahedral clusters [In₁₄Sn₂Zn₄Se₃₅]^12- with visible-light-driven selectively photocatalytic degradation activity. Single-crystal XRD analysis shows that compound 1 crystallizes in I4₁/acd (no. 142) space group, with a = b = 24.3462(2) Å, c = 45.0062(9) Å, V = 26676.9(7) ų, and Z = 8. Under visible-light irradiation, the selectively photocatalytic activities of 1 were evaluated by photodegradation of two kinds of cationic dye molecules, i.e., methylene blue (MB) and rhodamine B (RhB), against two anionic dyes, methyl orange (MO) and Kermes red (KR), with different sizes. We show that the adsorption capability and charge-matching between organic dyes and the supertetrahedral cluster together with a suitable band structure make it an excellent and selective photocatalyst. This is the first example of an open-framework chalcogenide based on supertetrahedral T4 for the selectively semiconductor photocatalytic decomposition of organic dyes.

Bimetallic PtAu Alloy Nanoparticles-Integrated g-C3N4 Hybrid as an Efficient Photocatalyst for Water-to-Hydrogen Conversion

Herein, we report the synthesis of metal (Pt and Au) and metal alloy (PtAu) nanoparticles (NPs)-integrated graphitic carbon nitride (g-C₃N₄) hybrids using a facile solvothermal route for water-splitting application. The metal and metal alloy NPs with varying percentages of Pt and Au are found to be in the size range of 3-5 nm and uniformly distributed on the g-C₃N₄ sheets. The metal and metal alloy NPs act as cocatalyst for g-C₃N₄ to enhance the photocatalytic activity for hydrogen (H₂) generation through higher light absorption and efficient charge separation. The alloy composition plays an important role to maximize the photoactivity, with an optimized PtAu/g-C₃N₄ sample delivered 1009 μmol g^-1 h^-1 of H₂. The visible light assisted photocatalytic H₂ evolution is further investigated with the optimized PtAu alloy NPs-integrated g-C₃N₄. This study presents a robust, stable, and easily synthesizable PtAu/g-C₃N₄ hybrid material as a promising photocatalyst for H₂ generation through water splitting.

Photocatalytic degradation of metronidazole and methylene blue by PVA-assisted Bi2WO6–CdS nanocomposite film under visible light irradiation

The enhanced photocatalytic performance of nanocomposite is synthesized via the hydrothermal method and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) and photoluminescence spectroscopy (PL). Under visible light irradiation, PVA assisted Bi2WO6–CdS nanocomposite film displayed enhanced photocatalytic efficiency and inhibition of photocorrosion as compared with pure CdS, pure Bi2WO6 and Bi2WO6–CdS composite. The PVA assisted Bi2WO6–CdS composite film catalyst showed stable catalytic performance until seven successive runs with 92% of methylene blue(MB) degradation, and easy to recover after degradation of organic pollutant. PVA assisted Bi2WO6–CdS nanocomposite film has optimal band edge position for superior photocatalytic degradation. Furthermore, the trapping experiment was carried out using different scavenger for active species. Among the active species, OH· are the most responsive species which play a vital role in the degradation of metronidazole and MB.

Fabrication of Bi2S3/ZnO heterostructures: an excellent photocatalyst for visible-light-driven hydrogen generation and photoelectrochemical properties

Bi₂S₃/ZnO heterostructures were synthesized, showing a high catalytic effect in photocatalytic hydrogen generation and organic dye degradation under visible light.