Synergistic Enhancement of CO2 photoreduction through sulfur defects in (3D/2D) CdS-nanoflowers/CN Binary heterojunction photocatalyst under visible light

Global warming is the biggest threat to the entire world owing to the continuous release of greenhouse gases such as CO2 from various sources. Herein, we have utilized renewable energy for the conversion of CO2 to valuable feedstocks through a semiconductor-mediated photocatalytic system. The cadmium sulfide nanoflowers (CS-NFs) decorated graphitic carbon nitride (CN) through a solvothermal route to form a Z-scheme CSCN heterojunction. The as-synthesized material has been characterized by various spectroscopic and microscopic tools. The optimal CSCN-0.5 (1:0.5) photocatalyst achieves a CO production rate of 130.9 μmol g-1 under visible light irradiation of 4h (λ > 420 nm), doubling that of pristine CS-NFs and CN. CO, along with CH4 (3.4 μmol g-1) and C2H6 (2.9 μmol g-1), is the sole product detected. Experimental results indicate that the CSCN-0.5 photocatalyst spatially separates electron-hole pairs, suppresses charge carrier recombination, and maintains robust redox ability, enhancing CO2 photoreduction. The CO2 reduction mechanism over CSCN heterojunction was also studied through in-situ DRIFTS and electron spin resonance (ESR) measurements. Therefore, CSCN proves that it could be used as a robust photocatalyst for the CO2 reduction reactions towards C1 and C2 feedstocks.

Recent Advances in Photocatalytic Oxidation of Methane to Methanol

Methane is one of the promising alternatives to non-renewable petroleum resources since it can be transformed into added-value hydrocarbon feedstocks through suitable reactions. The conversion of methane to methanol with a higher chemical value has recently attracted much attention. The selective oxidation of methane to methanol is often considered a “holy grail” reaction in catalysis. However, methanol production through the thermal catalytic process is thermodynamically and economically unfavorable due to its high energy consumption, low catalyst stability, and complex reactor maintenance. Photocatalytic technology offers great potential to carry out unfavorable reactions under mild conditions. Many in-depth studies have been carried out on the photocatalytic conversion of methane to methanol. This review will comprehensively provide recent progress in the photocatalytic oxidation of methane to methanol based on materials and engineering perspectives. Several aspects are considered, such as the type of semiconductor-based photocatalyst (tungsten, titania, zinc, etc.), structure modification of photocatalyst (doping, heterojunction, surface modification, crystal facet re-arrangement, and electron scavenger), factors affecting the reaction process (physiochemical characteristic of photocatalyst, operational condition, and reactor configuration), and briefly proposed reaction mechanism. Analysis of existing challenges and recommendations for the future development of photocatalytic technology for methane to methanol conversion is also highlighted.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Low-Dimensional Nanostructured Photocatalysts for Efficient CO2 Conversion into Solar Fuels

The ongoing energy crisis and global warming caused by the massive usage of fossil fuels and emission of CO2 into atmosphere continue to motivate researchers to investigate possible solutions. The conversion of CO2 into value-added solar fuels by photocatalysts has been suggested as an intriguing solution to simultaneously mitigate global warming and provide a source of energy in an environmentally friendly manner. There has been considerable effort for nearly four decades investigating the performance of CO2 conversion by photocatalysts, much of which has focused on structure or materials modification. In particular, the application of low-dimensional structures for photocatalysts is a promising pathway. Depending on the materials and fabrication methods, low-dimensional nanomaterials can be formed in zero dimensional structures such as quantum dots, one-dimensional structures such as nanowires, nanotubes, nanobelts, and nanorods, and two-dimensional structures such as nanosheets and thin films. These nanostructures increase the effective surface area and possess unique electrical and optical properties, including the quantum confinement effect in semiconductors or the localized surface plasmon resonance effect in noble metals at the nanoscale. These unique properties can play a vital role in enhancing the performance of photocatalytic CO2 conversion into solar fuels by engineering the nanostructures. In this review, we provide an overview of photocatalytic CO2 conversion and especially focus on nanostructured photocatalysts. The fundamental mechanism of photocatalytic CO2 conversion is discussed and recent progresses of low-dimensional photocatalysts for efficient conversion of CO2 into solar fuels are presented.