A Direct Z-Scheme for the Photocatalytic Hydrogen Production from a Water Ethanol Mixture on CoTiO3/TiO2 Heterostructures

Advances in the heterostructures for enhanced hydrogen production efficiency: a comprehensive review

The growing global energy demand and heightened environmental consciousness have contributed to the increasing interest in green energy sources, including hydrogen production. However, the efficacy of this technology is contingent upon the efficient separation of charges, high absorption of sunlight, rapid charge transfer rate, abundant active sites and resistance to photodegradation. The utilization of photocatalytic heterostructures coupling two materials has proved to be effective in tackling the aforementioned challenges and delivering exceptional performance in the production of hydrogen. The present article provides a comprehensive overview of operational principles of photocatalysis and the combination of photocatalytic and piezo-catalytic applications with heterostructures, including the transfer behavior and mechanisms of photoexcited non-equilibrium carriers between the materials. Furthermore, the effects of recent advances and state-of-the-art designs of heterostructures on hydrogen production are discussed, offering practical approaches to form heterostructures for efficient hydrogen production.

Encapsulating stable perovskite catalysts in hollow nanoreactors for enhanced pollutants degradation

Creating a microenvironment for enhanced peroxymonosulfate (PMS) activation is vital in advanced oxidation processes. The objective of this study was to fabricate nanoshells composed of titanium dioxide embedded with cobalt titanate nanoparticles of perovskite to act as nanoreactors for effectively initiating PMS and degrading contaminants. The unique porous structure and confined space of the nanoreactor facilitated reactant absorption and mass transfer to the active sites, resulting in exceptional catalytic performance for pollutant elimination. Experimental findings revealed close to 100% decomposition efficiency of 4-chlorophenol (4-CP) within an hour utilizing the nanoreactors over a wide pH range. The TiO2/CoTiO3 hollow nanoshells catalysts also displayed adaptability in disintegrating organic dyes and antibiotics. The radicals SO4•-, •OH, and non-radicals 1O2 were determined to be accountable for eliminating pollutants, as supported by trapping experiments and electron paramagnetic resonance spectra. The catalyst was confirmed as an electron donor and PMS as an electron acceptor through electrochemical tests and density functional theory calculations. This study underscores the potential of incorporating stable perovskite catalysts in hollow nanoreactors to enhance wastewater treatment.

Solar-Driven Biomass Reforming for Hydrogen Generation: Principles, Advances, and Challenges

Hydrogen (H2) has emerged as a clean and versatile energy carrier to power a carbon-neutral economy for the post-fossil era. Hydrogen generation from low-cost and renewable biomass by virtually inexhaustible solar energy presents an innovative strategy to process organic solid waste, combat the energy crisis, and achieve carbon neutrality. Herein, the progress and breakthroughs in solar-powered H2 production from biomass are reviewed. The basic principles of solar-driven H2 generation from biomass are first introduced for a better understanding of the reaction mechanism. Next, the merits and shortcomings of various semiconductors and cocatalysts are summarized, and the strategies for addressing the related issues are also elaborated. Then, various bio-based feedstocks for solar-driven H2 production are reviewed with an emphasis on the effect of photocatalysts and catalytic systems on performance. Of note, the concurrent generation of value-added chemicals from biomass reforming is emphasized as well. Meanwhile, the emerging photo-thermal coupling strategy that shows a grand prospect for maximally utilizing the entire solar energy spectrum is also discussed. Further, the direct utilization of hydrogen from biomass as a green reductant for producing value-added chemicals via organic reactions is also highlighted. Finally, the challenges and perspectives of photoreforming biomass toward hydrogen are envisioned.

Facet-engineered TiO2 drives photocatalytic activity and stability of supported noble metal clusters during H2 evolution

Metal clusters supported on TiO2 are widely used in many photocatalytic applications, including pollution control and production of solar fuels. Besides high photoactivity, stability during the photoreaction is another essential quality of high-performance photocatalysts, however systematic studies on this attribute are absent for metal clusters supported on TiO2. Here we have studied, both experimentally and with first-principles simulation methods, the stability of Pt, Pd and Au clusters prepared by ball milling on nanoshaped anatase nanoparticles preferentially exposing {001} (plates) and {101} (bipyramids) facets during the photogeneration of hydrogen. It is found that Pt/TiO2 exhibits superior stability than Pd/TiO2 and Au/TiO2, and that {001} facet-based photocatalysts always are more stable than their {101} analogous regardless of the considered metal species. The loss of stability associated with cluster sintering, which is facilitated by the transfer of photoexcited carriers from the metal species to the neighbouring Ti and O atoms, most significantly and detrimentally affects the H2-evolution photoactivity.

Urea-H2O2 defect engineering of δ-MnO2 for propane photothermal oxidation: Structure-activity relationship and synergetic mechanism determination

Photothermal catalysis has an advantage in effective and economical elimination technology of volatile organic compounds (VOCs) in the ascendant. Herein, various surface defect engineering routes were adopted to enhance the low-temperature propane oxidation of δ-MnO₂. Compared to reducing etchants urea and vitamin C, δ-MnO₂ treated with urea - H₂O₂ exhibited an excellent thermal (T₉₀ = 240 ℃) and photothermal (T₉₀ = 196 ℃) activities of propane oxidation. Urea - H₂O₂ treatment provided high concentration of Mn⁴⁺ and surface-active oxygen (Mn⁴⁺-O_sur) species as surface-active sites, and produced numerous oxygen vacancies to improve charge separation and superoxide species generation capacity. Thus, the photothermal conversion efficiency and low-temperature reducibility were remarkably enhanced. Furthermore, the photothermal synergistic catalytic mechanism was proposed based on in-situ diffuse reflectance infrared Fourier transform spectroscopy and control experiments. The strategy here offered insight into the rational design of efficient transition catalysts, and in-depth understanding of the photothermal catalytic VOCs removal mechanism.

0D/2D Co0.85Se/TiO2 p–n heterojunction for enhanced photocatalytic H2 evolution

The H2 rate of 15%-Co0.85Se/TiO2 is 2312.5 μmol g−1 h−1, which is 10.3 times and 10.8 times higher than TiO2 and Co0.85Se. The enhanced activity is attributed to the higher electrochemically active surface area and the formation of p–n heterostructure.

Photodehydrogenation of Ethanol over Cu2O/TiO2 Heterostructures

The photodehydrogenation of ethanol is a sustainable and potentially cost-effective strategy to produce hydrogen and acetaldehyde from renewable resources. The optimization of this process requires the use of highly active, stable and selective photocatalytic materials based on abundant elements and the proper adjustment of the reaction conditions, including temperature. In this work, Cu₂O-TiO₂ type-II heterojunctions with different Cu₂O amounts are obtained by a one-pot hydrothermal method. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The Cu₂O-TiO₂ photocatalysts exhibit a high selectivity toward acetaldehyde production and up to tenfold higher hydrogen evolution rates compared to bare TiO₂. We further discern here the influence of temperature and visible light absorption on the photocatalytic performance. Our results point toward the combination of energy sources in thermo-photocatalytic reactors as an efficient strategy for solar energy conversion.

In situ construction of a direct Z-scheme CdIn2S4/TiO2 heterojunction for improving photocatalytic properties

Direct Z-scheme photocatalytic systems driven by visible light to eliminate organic pollutants in wastewater have become important scientific tools in the field of photocatalysis.