Onion-Ring-like Carbon and Nitrogen from ZIF-8 on TiO2/Fe2O3 Nanostructure for Overall Electrochemical Water Splitting

TiO2 nanorod decorated with MoS2 nanospheres: An efficient dual-functional photocatalyst for antibiotic degradation and hydrogen production

The design and preparation of dual-functional photocatalysts for simultaneously realizing photocatalytic wastewater purification and hydrogen energy generation pose significant challenges. This article presents the engineering of a binary heterostructured photocatalyst by combining TiO2 (nanorods) and MoS2 nanosphere using a straightforward solvothermal method and the assessment of the phase structures, morphologies, and optical properties of the resulting nanocomposites using diverse analytical techniques. The TiO2(Rod)/MoS2 composite exhibits remarkable efficacy in degrading ciprofloxacin, achieving 93% removal rate within 1 h, which is four times higher than that of bare TiO2. Moreover, the optimized TiO2(Rod)/MoS2 presents an outstanding hydrogen production rate of 7415 μmol g-1, which is ∼24 times higher than that of pristine TiO2. Under UV-visible light irradiation, the TiO2(Rod)/MoS2 heterojunction displays an exceptional photocatalytic performance in terms of both photodegradation and hydrogen production, surpassing the performance of TiO2 particle/MoS2. The study findings demonstrate that TiO2(Rod)/MoS2 nanocomposites exhibit considerably improved photocatalytic degradation and hydrogen generation activities. Based on the experimental results, a possible mechanism is proposed for the transfer and separation of charge carriers in Z-scheme heterojunctions.

Interface Charge Distribution Engineering of Pd-CeO2 /C for Efficient Carbohydrazide Oxidation Reaction

Carbohydrazide electrooxidation reaction (COR) is a potential alternative to oxygen evolution reaction in water splitting process. However, the sluggish kinetics process impels to develop efficient catalysts with the aim of the widespread use of such catalytic system. Since COR concerns the adsorption/desorption of reactive species on catalysts, the electronic structure of electrocatalyst can affect the catalytic activity. Interface charge distribution engineering can be considered to be an efficient strategy for improving catalytic performance, which facilitates the cleavage of chemical bond. Herein, highly dispersed Pd nanoparticles on CeO2 /C catalyst are prepared and the COR catalytic performance is investigated. The self-driven charge transfer between Pd and CeO2 can form the local nucleophilic and electrophilic region, promoting to the adsorption of electron-withdrawing and electron-donating group in carbohydrazide molecule, which facilitates the cleavage of C-N bond and the carbohydrazide oxidation. Due to the local charge distribution, the Pd-CeO2 /C exhibits superior COR catalytic activity with a potential of 0.27 V to attain 10 mA cm-2 . When this catalyst is used for energy-efficient electrolytic hydrogen production, the carbohydrazide electrolysis configuration exhibits a low cell voltage (0.6 V at 10 mA cm-2 ). This interface charge distribution engineering can provide a novel strategy for improving COR catalytic activity.

Fe2O3/Ni Nanocomposite Electrocatalyst on Cellulose for Hydrogen Evolution Reaction and Oxygen Evolution Reaction

A key challenge in the development of sustainable water-splitting (WS) systems is the formulation of electrodes by efficient combinations of electrocatalyst and binder materials. Cellulose, a biopolymer, can be considered an excellent dispersing agent and binder that can replace high-cost synthetic polymers to construct low-cost electrodes. Herein, a novel electrocatalyst was fabricated by combining Fe2O3 and Ni on microcrystalline cellulose (MCC) without the use of any additional binder. Structural characterization techniques confirmed the formation of the Fe2O3-Ni nanocomposite. Microstructural studies confirmed the homogeneity of the ~50 nm-sized Fe2O3-Ni on MCC. The WS performance, which involves the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), was evaluated using a 1 M KOH electrolyte solution. The Fe2O3-Ni nanocomposite on MCC displayed an efficient performance toward lowering the overpotential in both the HER (163 mV @ 10 mA cm-2) and OER (360 mV @ 10 mA cm-2). These results demonstrate that MCC facilitated the cohesive binding of electrocatalyst materials and attachment to the substrate surface. In the future, modified cellulose-based structures (such as functionalized gels and those dissolved in various media) can be used as efficient binder materials and alternative options for preparing electrodes for WS applications.

Approach to Evaluation of Electrocatalytic Water Splitting Parameters, Reflecting Intrinsic Activity: Toward the Right Pathway

The development of transition metal-based non-precious-metal electrocatalysts for energy storage and conversion systems has received a lot of interest recently. To further this subject in the proper way given the development of electrocatalysts, a fair comparison of their respective performance is necessary. This Review investigates the parameters used for the comparison of electrocatalyst activity. Significant evaluation criteria employed in electrochemical water splitting studies are the overpotential at defined current density usually at 10 mA per geometric surface area, Tafel slope, exchange current density, mass activity, specific activity and turnover frequency (TOF). This Review will discuss how to identify the specific activity and TOF by electrochemical and non-electrochemical methods to represent intrinsic activity as well as the benefits and uncertainties of each technique, ensuring that each method is applied correctly when calculating intrinsic activity metrics.

Synthesis of Ce and Sm Co-Doped TiO2 Nanoparticles with Enhanced Photocatalytic Activity for Rhodamine B Dye Degradation

One of the major concerns that receive global attention is the presence of organic pollutants (dyes, pharmaceuticals, pesticides, phenolic compounds, heavy metals, and so on), originating from various industries, in wastewater and water resources. Rhodamine B is widely used in the dyeing of paints, plastics, textiles, and other fabrics, as well as biological products. It is highly persistent, toxic, and carcinogenic to organisms and humans when directly released into the water supply. To avoid this hazard, several studies have been conducted in an attempt to remove Rhodamine B from wastewater. Metal oxide semiconducting materials have gained great interest because of their ability to decompose organic pollutants from wastewater. TiO2 is one of the most effective photocatalysts with a broad range of applications. Several attempts have been made to improve its photocatalytic activity. Accordingly, we have prepared in this work a series of cerium (Ce) and samarium (Sm) co-doped TiO2 nanoparticles (x = 0.00, 0.25, 0.50, 1.00, and 2.00%) using a sol–gel auto-combustion approach. The influence of Ce–Sm concentrations on the structural, morphology, electronic, and optical properties, as well as the photocatalytic activity, was investigated. Structure and elemental mapping analyses proved the presence of Ce and Sm in the compositions as well as the development of the TiO2 anatase phase with a tetragonal structure and crystallite size of 15.1–17.8 nm. Morphological observations confirmed the creation of spherical nanoparticles (NPs). The examination of the electronic structure properties using density functional theory (DFT) calculations and of the optical properties using a UV/Vis diffuse spectrophotometer showed a reduction in the bandgap energy upon Ce–Sm co-doping. The photocatalytic activity of the synthesized products was assessed on the degradation of Rhodamine B dye, and it was found that all Ce–Sm co-doped TiO2 nanoparticles have better photocatalytic activities than pristine TiO2 nanoparticles. Among all of the prepared nanoparticles, the sample with x = 0.50% demonstrated the best photocatalytic activity, with a degradation efficiency of 98% within 30 min and a reaction rate constant of about 0.0616 min−1. h+ and •O2− were determined to be the most important active species in the photocatalytic degradation process. Besides the high photocatalytic degradation efficiency, these photocatalysts are highly stable and could be easily recovered and reused, which indicates their potential for practical applications in the future.

Insight into the Mechanism for Catalytic Activity of the Oxygen/Hydrogen Evolution Reaction on a Dual-Site Catalyst

The dual-site catalysts consisting of two adjacent single-atom sites on graphene have exhibited promising catalytic activity of the electrochemical oxygen/hydrogen evolution reaction (OER/HER). However, the electrochemical mechanisms of the OER/HER on dual-site catalysts have still been ambiguous. In this work, we employed density functional theory calculations to study the catalytic activity of the OER/HER with a O-O (H-H) direct coupling mechanism on dual-site catalysts. Specifically, these element steps should be classified into two categories: a step evolving proton-coupled electron transfer (PCET step) that needs to be driven by electrode potential and a step without PCET (non-PCET step) that occurs naturally under mild conditions. Our calculated results show that both the maximal free energy change (ΔG_Max) contributed by the PCET step and the activity barrier (E_a) of the non-PCET step must be examined to evaluate the catalytic activity of the OER/HER on the dual site. Importantly, it is a basically inevitable negative relationship between ΔG_Max and E_a, which would play a critical role in guiding the rational design of effective dual-site catalysts for electrochemical reactions.

Metal ferrites-based nanocomposites and nanohybrids for photocatalytic water treatment and electrocatalytic water splitting

Photocatalytic degradation is one of the most promising technologies available for removing a variety of synthetic and organic pollutants from the environmental matrices because of its high catalytic activity, reduced energy consumption, and low total cost. Due to its acceptable bandgap, broad light-harvesting efficiency, significant renewability, and stability, Fe₂O₃ has emerged as a fascinating material for the degradation of organic contaminants as well as numerous dyes. This study thoroughly reviewed the efficiency of Fe₂O₃-based nanocomposite and nanomaterials for water remediation. Iron oxide structure and various synthetic methods are briefly discussed. Additionally, the electrocatalytic application of Fe₂O₃-based nanocomposites, including oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, and overall water splitting efficiency, was also highlighted to illustrate the great promise of these composites. Finally, the ongoing issues and future prospects are directed to fully reveal the standards of Fe₂O₃-based catalysts. This review is intended to disseminate knowledge for further research on the possible applications of Fe₂O₃ as a photocatalyst and electrocatalyst.

Synthesis and application of titanium dioxide photocatalysis for energy, decontamination and viral disinfection: a review

Global pollution is calling for advanced methods to remove contaminants from water and wastewater, such as TiO₂-assisted photocatalysis.  The environmental applications of titanium dioxide have started after the initial TiO₂ application for water splitting by Fujishima and Honda in 1972. TiO₂ is now used for self-cleaning surfaces, air and water purification systems, microbial inactivation and selective organic conversion. The synthesis of titanium dioxide nanomaterials with high photocatalytic activity is actually a major challenge. Here we review titanium dioxide photocatalysis with focus on mechanims, synthesis, and applications. Synthetic methods include sol-gel, sonochemical, microwave, oxidation, deposition, hydro/solvothermal, and biological techniques. Applications comprise the production of energy, petroleum recovery, and the removal of microplastics, pharmaceuticals, metals, dyes, pesticides, and of viruses such as the severe acute respiratory syndrome coronavirus 2.

Controlling the Fe2O3-SiO2 interaction: The effect on the H2S selective catalytic oxidation and catalyst deactivation

Biogas utilization is one of the most promising options for reducing the consumption of fossil fuels for energy production, but the presence of H₂S represents a serious industrial and environmental problem. In this work, two different synthesis methods (sol-gel and incipient wetness impregnation) were used to synthesize iron oxide supported on silica catalysts (Fe₂O₃/SiO₂) with metal loadings ranging from 0.5 to 10 %wt. The catalysts were tested for the selective oxidation of H₂S, changing the operating conditions like O₂/H₂S (0.5-2.5), temperature (170-250°C), and water content (0-50%). The optimum condition was O₂/H₂S = 0.5 and no water at 230 °C with the conversion of approximately 100%, the selectivity of 97%, and the deactivation of 0.6%. A detailed characterization of the fresh and spent catalysts' surface revealed the presence of four deactivation mechanisms: metal surface reduction, oxygen vacancy loss, pore plugging, and sintering. Among the observed deactivation mechanisms, the sintering showed the highest impact on catalytic activity and deactivation. The sol-gel catalysts (SG) showed the highest metal-oxide/support interaction, which reduced the metal-oxide nanoparticles sintering compared with the incipient wetness impregnation method (IWI), reporting a lower sintering, higher activity, and selectivity, lower deactivation rates and lower sensitivity to the operating conditions. A catalytic cycle representing the possible surface intermediate states of the catalyst is proposed based on the performance and characterization results obtained.

Bio-Inspired C/N/TiO2 Hybrid Composite Heterostructure: Enhanced Photocatalytic Activity under Visible Light

The hydrothermal treatment was used to create a natural hierarchical bio-inspired carbon and nitrogen-doped C/N/TiO2 hybrid composite. It is the goal of this work to investigate the photocatalytic activity of bio-inspired C/N/TiO2 hybrid composite. Techniques such as X-ray powder diffraction, scanning electron microscopy, UV-Vis absorption spectroscopy, FTIR, Raman, and photoluminescence spectroscopy were used to explore the structural, morphological, and photocatalysis characteristics of the bio-inspired C/N/TiO2 hybrid composite. By doping carbon and nitrogen, TiO2 nanotubes were able to improve the photocatalyst properties of the C/N/TiO2 hybrid composite, decrease the energy band gap (∼2.55 eV), and result in increased electron transfer efficiency when compared to pure TiO2. The photocatalytic degradation of pollutants (rhodamine B (RhB)) is made possible by the use of a bio-inspired C/N/TiO2 hybrid composite that has high interconnectivity and an easily accessible surface.

An eco-friendly and sustainable support of agave-fibers functionalized with graphene/TiO2:SnO2 for the photocatalytic degradation of the 2,4-D herbicide from the drinking water

In this research, we evaluated the photocatalytic performance of biodegradable composites for the removal of the 2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide. The composite was composed by agave fibers (AgF), graphene-microplates (GM) and titanium dioxide TiO₂/SnO₂ (TSn) nanoparticles (NPs) and was named TSn + AgF/GM. Both, the TSn NPs and the GM were deposited on the AgF using the Dip-coating method. According to the analysis by X-Ray Diffraction (XRD), the crystalline phase for the TiO₂ and SnO₂ was anatase and tetragonal-rutile, respectively. The Scanning Electron Microscopy (SEM) images demonstrated that the AgF were completely saturated by the GM (which had average dimensions of 15 μm × 22 μm) and by conglomerations of TSn NPs with average size of 642 nm. The TSn NPs and the TSn + AgF/GM composite were evaluated for the photocatalytic degradation of the 2,4-D herbicide under ultraviolet-visible (UV-Vis) light and found a maximum degradation of 98.4 and 93.7% (after 4 h) for the TSn NPs and the TSn + AgF/GM composite, respectively. Reuse cycles were also performed and the degradation percentage decreased by 13.1% and by 7.8% (after 3 cycles of reuse) when the TSn NPs and the TSn + AgF/GM composite are employed, respectively. Scavenger experiments were also carried out and found that the oxidizing agents are mainly produced in the order of: •OH>•O₂^- > h⁺; then, the main oxidizing agents generated during the photocatalytic reaction were the hydroxyl radicals. Thus, the photocatalytic system studied in this work for the degradation of 2,4-D could pave the way for the development of new eco-friendly/floatable photocatalysts, which can be applied in wastewater-treatment plants.

A review on sensitivity of operating parameters on biogas catalysts for selective oxidation of Hydrogen Sulfide to elemental sulfur

Hydrogen sulfide (H₂S) is a critical problem for biogas applications, such as electricity and heat generation, or the production of different chemical compounds, due to corrosion and toxic effluent gases. The selective catalytic oxidation of H₂S to S is the most promising way to eliminate H₂S from biogas due to the lack of effluents, therefore can be considered a green technology. The most extensively used catalysts for H₂S selective oxidation can be classified in two groups: metal oxide-based catalysts, including vanadium and iron oxides, and carbon-based catalysts. Numerous studies have been devoted to studying their different catalytic performances. For industrial applications, the most suitable catalysts should be less sensitive to the operating parameters like the temperature, O₂/H₂S ratio, and H₂O content. More specifically, for metal oxides and carbon-based catalysts, the temperature and O₂/H₂S ratio have a similar effect on the conversion and selectivity, but carbon-based catalysts are less sensitive to water in all operating conditions.

In2S3 nanoparticles coupled to In-MOF nanorods: The structural and electronic modulation for synergetic photocatalytic degradation of Rhodamine B

Enhancing photocatalytic performance via electronic modulation have attracted much attention for synergetic photocatalytic degradation of antibiotic pollutant. In this study, a new hetero-structured system is raised, which comprises In₂S₃ coupled to In-MOF and operates as an efficient photocatalyst for RhB degradation. The formation of hetero-structure and occurred electron modulation of In₂S₃/In-MOF hybrid was confirmed by relevant characterizations. Surprisingly, the In₂S₃/In-MOF hybrid represented enhanced photocatalytic ability over In-MOF. The photocatalysis of Rhodamine B in presence of In₂S₃/In-MOF hybrid has achieved 92.2 % degradation.

SnNb2O6/NiCo-LDH Z-scheme heterojunction with regulated oxygen vacancies obtained by engineering the crystallinity for efficient and renewable photocatalytic H2 evolution

SnNb2O6/NiCo-LDH Z-scheme heterojunction with abundant oxygen vacancies exhibited highly activity and stability toward photocatalytic H2 evolution, ascribed to the regeneration of oxygen vacancy by engineering the crystallinity.