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Improving the stability of cuprous oxide (Cu2 O) is imperative to its practical applications in artificial photosynthesis. In this work, Cu2 O nanowires are encapsulated by metal-organic frameworks (MOFs) of Cu3 (BTC)2 (BTC=1,3,5-benzene tricarboxylate) using a surfactant-free method. Such MOFs not only suppress the water vapor-induced corrosion of Cu2 O but also facilitate charge separation and CO2 uptake, thus resulting in a nanocomposite representing 1.9 times improved activity and stability for selective photocatalytic CO2 reduction into CH4 under mild reaction conditions. Furthermore, direct transfer of photogenerated electrons from the conduction band of Cu2 O to the LUMO level of non-excited Cu3 (BTC)2 has been evidenced by time-resolved photoluminescence. This work proposes an effective strategy for CO2 conversion by a synergy of charge separation and CO2 adsorption, leading to the enhanced photocatalytic reaction when MOFs are integrated with metal oxide photocatalyst.

The photocatalytic conversion of CO2 to energy-rich CH4 solar fuel is an ideal strategy for future energy generation as it can resolve global warming and the imminent energy crisis concurrently. Ho...

Light energy can be harnessed by photosensitizers or photocatalysts so that some chemical reactions can be carried out under milder conditions compared to the traditional heat-driven processes. To facilitate the photodriven reactions, a large variety of chromophores that operate via charge transfer excitations have been reported because of their typically longer excited-state lifetimes, which are key to the downstream photochemical processes. Although both metal-to-ligand charge transfers and ligand-to-metal charge transfers are well-established light absorption pathways, the former has been widely adopted in photocatalysis, whereas the latter has taken on greater importance in photosensitization applications only recently. In this article, we review the latest developments on ligand-to-metal charge transfer photosensitization by molecular complexes across the periodic table, with a focus on homogeneous photocatalysis and the use of photophysical measurements and computational calculations to understand the electronic structures, photochemical processes, structure-activity relationships, and reaction mechanisms. We also present our perspectives on the possible future developments in the field. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version H.S.S. acknowledges that this project is supported by A*STAR under the AME IRG grant A2083c0050. H.S.S. is also grateful for the Singapore Ministry of Education Academic Research Fund Tier 1 grant RT 05/19. H.S.S. and X.Y.K. thank the Singapore National Academy of Science (SNAS) and the National Research Foundation (NRF) Singapore for funding under its SNAS ASEAN Postdoctoral Fellowship (NRF-MP-2020-0001) program. Part of this work was also supported by the Nanyang Technological University 5th ACE grant call and the 2021 American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable Ignition Grant. Z.H.T thanks the Nanyang Technological University - CN Yang Scholars Program for financial support.

The incorporation of cobalt phosphide (CoP) as a noble-metal-free co-catalyst onto Zn0.5Cd0.5S with a unique zinc blende/wurtzite (ZB/WZ)-homojunction structure (ZCS) has resulted in significantly enhanced photocatalytic activity. The optimized sample, 3CoP–ZCS, yielded an exciting 20-times enhancement in H2 evolution (∼4.9 mmol h−1 g−1) over pristine ZCS under visible light irradiation. The enhancement was ascribed to the synergistic interaction between the ZB/WZ homojunctions and the close heterojunction formed between ZCS and CoP. Besides being able to effectively suppress the electron–hole recombination, the introduction of CoP was also proven to boost the light absorption ability of the composite in the visible light region. Owing to these beneficial aspects, it was evident that CoP serves as an efficient co-catalyst for photocatalytic H2 evolution.

Although perovskites have been proven to exhibit extraordinary performance in solar cell applications, the potential of perovskites in photocatalysis is yet to be fully explored. In particular, the unique properties of perovskite materials including chemical and optical stabilities, tunable bandgaps and crystal structures, long charge carrier lifetime and favorable band alignment make them a potential next generation photocatalyst. Considering that, a perspective on the state-of-the-art developments in perovskite-based photocatalysts and the modification strategies, i.e. defect engineering, doping or co-doping with metals or non-metals, sensitization, and facet control, is timely. This paper details perovskite-based photocatalysts for artificial photosynthesis, namely photocatalytic carbon dioxide (CO2) reduction and water splitting. In this perspective, perovskites are divided into four groups based on the B site element, namely titanates, tantalates, niobates and ferrites. The synthesis parameters and factors affecting the efficiency of photocatalysts are discussed. Finally, this perspective outlines the recent development of perovskite-based photocatalysts and the immense prospects that it presents when an appropriate modification technique is employed.

Semiconductor-based photocatalytic CO2 conversion is a promising and sustainable avenue in response to the anthropogenic climate change and imminent energy crisis, which however is unavoidably impeded by the limited photo-absorption, undesirable recombination of photogenerated charge carriers and insufficient surface active sites on semiconductors. In this study, all these challenges were overcome by selectively and chemically assembly of oxygen-deficient Bi2WO6 nanosheets onto BiOI nanosheets, forming a novel surface defect-engineered 2D/2D motif with built-in nanoscale p-n heterojunctions. This rational cascade configuration with internal electric field renders ultrafast directional migration and spatial separation of photogenerated charge carriers. Meanwhile, the oxygen vacant sites with abundant trapped electrons serve as the active sites for CO2 reduction and extend the light absorption of the photocatalytic system to NIR region. Combining these propitious properties, our delineated nanoscale p-n heterojunction on the basis of 2D/2D assembly of surface defect-engineered nanosheets presents a new and unprecedented concept for effective generation of charge carriers, directional steering of charge flow and manipulation of surface active sites, which cooperatively lead to superior photocatalytic performance. Notably, our developed oxygen-deficient Bi2WO6/BiOI binanosheets exhibit a remarkably high production yield of CH4, which represents the state-of-the-art visible light-driven CH4 production activity among all the existing 2D BiOI-based and Bi2WO6-based composites.

The management of plastics waste is one of the most urgent and significant global problems now. Historically, waste plastics have been predominantly discarded, mechanically recycled, or incinerated for energy production. However, these approaches typically relied on thermal processes like conventional pyrolysis, which are energy-intensive and unsustainable. In this Minireview, we discuss some of the latest advances and future trends in the chemical upcycling of waste plastics by photocatalytic, electrolytic, and microwave-assisted pyrolysis processes as more environmentally-friendly alternatives to conventional thermal reactions. We highlight how the transformation of different types of plastics waste by exploiting alternative energy sources can generate value-added products such as fuels (H2 and other carbon-containing small molecules), chemical feedstocks, and newly functionalized polymers, which can contribute to a more sustainable and circular economy. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Accepted version H.S.S. acknowledges that this project is supported by A*STAR under the AME IRG grants A2083c0050, A1783c0003, and A1783c0002. H.S.S. is also grateful for the Singapore Ministry of Education Academic Research Fund Tier 1 grant RT 05/19. H.S.S. and X.Y.K. acknowledge that this research is supported by the Singapore National Academy of Science (SNAS) and the National Research Foundation (NRF) Singapore under its SNAS ASEAN Postdoctoral Fellowship (NRF-MP-2020-0001) program.

Morphological control and surface vacancy modulation are effective strategies for promoting the readiness level of g-C3N4-based photocatalytic systems. In this work, we present an unprecedented proof-of-concept study on the doping effect of nitrogen vacancies in g-C3N4 atomic layers for enhanced CO2 photoreductivity. A 3D bubbly architecture scaffolded by few-atomic-layer (ca. 1.6 nm) g-C3N4 nanosheets with the potential to facilitate charge transportation was successfully realized by inducing a disruption in the π–π interactions between adjacent layers of g-C3N4 through simple incorporation of an NH4Cl gas template. Introduction of nitrogen vacancy defects into the ultrathin nanosheets further exerted remarkable tuning effects on their optoelectronic properties. The concomitant outcomes from the event of nitrogen vacancy introduction gave rise to several phenomena, including: (i) an increase in reducing ability with a higher nitrogen vacancy density, (ii) extended absorptivity to the long-wavelength visible light region due to the strategic band position of the midgap state below the CB, and (iii) prolonged radiative recombination of photogenerated electron–hole pairs, as the midgap state serves as an effective reservoir to temporarily trap electrons. As a result, the photoreduction performance of nitrogen defect-modified g-C3N4 atomic layers was synergistically improved with 3.16-fold and 5.14-fold enhancements in the CH4 evolution yield over their respective pristine ultrathin counterpart and bulk form.

Molybdenum disulfide quantum dots (MoS2QDs) decorated bismuth sulfide (Bi2S3) photocatalyst was synthesized. Photoluminescence characterization showed that the as-developed MoS2QDs possessed intriguing up-conversion and down-conversion properties, indicating their capability to harness energy from the light spectrum ranging from ultraviolet (UV) to near-infrared (NIR). In this study, the highest hydrogen yield of 17.7 mmol/g.h was achieved by 0.14MoS2QD/Bi2S3, which was almost 4.5 folds higher than that of undoped Bi2S3 under stimulated solar light irradiation. Furthermore, examination of the 0.14MoS2QD/Bi2S3 photocatalysts under NIR irradiation showed a significant photocurrent response and an accumulative H2 yield of 53.6 μmol/g after 6 h reaction. This is a major breakthrough as most photocatalysts can only be activated under UV and/or visible light irradiation. This work provides new insights into the design of MoS2QD/Bi2S3 for harnessing energy from a broad solar spectrum to photocatalytically split water to produce hydrogen.

Under the tremendous pressure of imminent energy crisis and anthropogenic climate change, photocatalytic conversion of abandoned CO2 into energy-rich hydrocarbon fuels is highly desirable. However, this solar-to-fuel conversion is unavoidably suppressed by the fast recombination of electron-hole pairs and lack of stability of photocatalysts. To overcome this, we have developed ultrathin BiOBr nanosheets (BOB-NS) with primarily exposed {001} facets. The {001} facets of BOB-NS are comprised of high density O atoms, which are linked to the neighbouring Bi atoms via weak Bi O bonds with long bond length and low bond energy. After visible-light-driven CO2 photoreduction over BOB-NS, we found that the Bi O bonds were broken and oxygen vacancy (OV) defects formed on the sample surface. The presence of these OVs was proven to be beneficial for photoactivities as photoinduced electrons were effectively trapped at the OV sites and recombination of charge carriers were inhibited. Generally, the free O atoms from dissociation of CO2 would reoxidize the sample surface, thereby deteriorating the performance of photocatalysts. In contrast, we demonstrated in this study that the OV sites on BOB-NS could be simultaneously regenerated and refreshed as the reactions proceeded, leading to a sustainable activity and long-term stability for CO2 photoreduction.

Pseudobinary ZnxCd1-xS semiconductor with zinc blende/wurtzite (ZB/WZ) twin-induced crystal structure has been regarded as one of the best pristine sulfide photocatalysts for H2 evolution via water splitting. While the synthesis of this nano-twin photocatalyst is at the forefront of research, the incorporation of co-catalyst to improve photocatalytic activities through synergistic properties has rarely been reported. Loading well-dispersed ultrasmall platinum (Pt) with controlled sizes is the pivotal element in maximizing atom-utilization efficiencies by downsizing the noble metal clusters. In this contribution, we report the fabrication of highly dispersed sub-2 nm Pt decorated twinned Zn0.5Cd0.5S nanocrystals and their excellent photocatalytic H2 evolution in both acidic and alkaline sacrificial reagents. The high visible-light-driven H2 evolution rates of the most active sample (denoted as 8Pt-Zn0.5Cd0.5S) in 0.1 M Na2S/0.1 M Na2SO3 (pH = 12.94) and 0.15 M ascorbic acid (pH = 2.24) are measured to be 114.3 μmol h−1 (AQY:7.15%) and 164.9 μmol h−1 (AQY:8.56%), respectively, which render ca. 4.9- and 27.9-fold enhancement over pristine twinned Zn0.5Cd0.5S. The presence of homojunctions (within ZB and WZ segments) and heterojunctions (between Pt and twinned Zn0.5Cd0.5S) impart an efficient spatial charge separation and provide more active sites for highly efficient photocatalytic H2 production.

As the world decides on the next giant step for the renewable energy revolution, scientists have begun to reinforce their headlong dives into the exploitation of solar energy. Hitherto, numerous attempts are made to imitate the natural photosynthesis of plants by converting solar energy into chemical fuels which resembles the “Z‐scheme” process. A recreation of this system is witnessed in artificial Z‐scheme photocatalytic water splitting to generate hydrogen (H2). This work outlines the recent significant implication of the Z‐scheme system in photocatalytic water splitting, particularly in the role of electron mediator and the key factors that improve the photocatalytic performance. The Review begins with the fundamental rationales in Z‐scheme water splitting, followed by a survey on the development roadmap of three different generations of Z‐scheme system: 1) PS‐A/D‐PS (first generation), 2) PS‐C‐PS (second generation), and 3) PS‐PS (third generation). Focus is also placed on the scaling up of the “leaf‐to‐tree” challenge of Z‐scheme water splitting system, which is also known as Z‐scheme photocatalyst sheet. A detailed investigation of the Z‐scheme system for achieving H2 evolution from past to present accompanied with in‐depth discussion on the key challenges in the area of Z‐scheme photocatalytic water splitting are provided., The significant implication of Z‐scheme systems of different generations in photocatalytic water splitting, from past to present, is outlined and reviewed. The rationales and mechanisms in Z‐scheme systems, followed by a survey on the development roadmap of Z‐scheme systems from the first to third generation are presented. Lastly, the rapid emergence of particulate Z‐scheme photocatalyst sheets is outlined.

The photocatalytic reduction of CO2 to energy-rich hydrocarbon fuels is a promising and sustainable method of addressing global warming and the imminent energy crisis concomitantly. However, a vast majority of the existing photocatalysts are only capable of harnessing ultraviolet (UV) or/and visible light (Vis), whereas the near-infrared (NIR) region still remains unexplored. In this study, carbon quantum dots (CQDs)-decorated ultrathin Bi2WO6 nanosheets (UBW) were demonstrated to be an efficient photocatalyst for CO2 photoreduction over the Vis–NIR broad spectrum. It is noteworthy that the synthesis procedure of the CQDs/UBW hybrid nanocomposites was highly facile, involving a one-pot hexadecyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. Under visible light irradiation, the optimized 1CQDs/UBW (1 wt.% CQD content) exhibited a remarkable 9.5-fold and 3.1-fold enhancement of CH4 production over pristine Bi2WO6 nanoplatelets (PBW) and bare UBW, respectively. More importantly, the photocatalytic responsiveness of CQDs/UBW was successfully extended to the NIR region, which was achieved without involving any rare earth or noble metals. The realization of NIR-driven CO2 reduction could be attributed to the synergistic effects of (i) the ultrathin nanostructures and highly exposed {001} active facets of UBW, (ii) the excellent spectral coupling of UBW and CQDs, where UBW could be excited by the up-converted photoluminescence of CQDs, and (iii) the electron-withdrawing nature of the CQDs to trap the photogenerated electrons and retard the recombination of charge carriers.

A highly facile one-pot ethylene glycol-assisted solvothermal process was employed to fabricate bismuth oxybromide (BiOBr) with oxygen-deficient defects. These defects played an indispensable role for superior photocatalytic CO2 reduction, in which the as-prepared sample demonstrated a remarkable improvement of 3.3 and 5.7-fold for CH4 production over pristine BiOBr and P25, respectively. The enhancement could be attributed to the presence of oxygen vacancies, which acted as the active sites for CO2 adsorption and activation. In addition, the oxygen–deficiency–induced defect states could effectively trap photogenerated electrons, thus improving the separation of the electron–hole pairs and significantly slow down the recombination rate of charge carriers. On top of that, oxygen-deficient BiOBr exhibited long term stability (>50 hours of catalytic reaction) for CO2 photoreduction under simulated solar light, where no reducing agent or any post-treatment was needed to regenerate the oxygen vacancies.

Cutting edge research within solar energy harvesting focuses on H2 production from photocatalytic overall water splitting (OWS) using artificial two-step photoexcitation system known as Z-scheme. Inspired by natural photosynthesis, Z-scheme imparts a unique vectorial electron transfer from the ingenious arrangement of PS I-PS II coupling connected by an electron mediator. This allows Z-scheme to confer efficient charge isolation and split water into its constituent components, hydrogen (H2) and oxygen (O2), at two different positions with strong redox ability. More recently, particulate Z-scheme photocatalyst sheets have been worth noting as potentially scalable approach for solar water splitting. In this contribution, particulate Z-scheme photocatalyst sheets were developed using P-doped twinned Zn0.5Cd0.5S1-x (d-ZCS-P) as hydrogen evolution photocatalysts (HEP) and Bi4NbO8Cl as oxygen evolution photocatalysts (OEP), which both embedded on N-doped carbon nanotubes (N-CNTs) as carbon conductive film. Further surface modification on photocatalyst sheets through concerted deposition of co-catalyst and protective shell warrants an efficient overall water splitting from pure water, with a solar-to-hydrogen conversion efficiency (STH) of 0.15% under ambient condition. The rational Z-scheme configuration of photocatalyst sheets alleviates the effect of H+ and OH− concentration overpotentials which in turn bolstering the photocatalytic performance and paves a promising way of solar energy augmentation.

Photocatalytic CO2 reduction over the UV-Vis-NIR broad spectrum was realized for the first time. The presence of surface oxygen vacancy defects on Bi2WO6 resulted in significant photocatalytic enhancement over the pristine counterpart under UV and visible light irradiation. Meanwhile, the photocatalytic responsiveness of Bi2WO6-OV was successfully extended to the NIR region.

In the present work, two-dimensional bismuth oxybromide (BiOBr) was synthesized and coupled with co-catalyst molybdenum disulphide (MoS2) via a simple hydrothermal process. The photoactivity of the resulting hybrid photocatalyst (MoS2/BiOBr) was evaluated under the irradiation of 15 W energy-saving light bulb at ambient condition using Reactive Black 5 (RB5) as model dye solution. The photo-degradation of RB5 by BiOBr loaded with 0.2 wt% MoS2 (MoBi-2) exhibited more than 1.4 and 5.0 folds of enhancement over pristine BiOBr and titanium dioxide (Degussa, P25), respectively. The increased photocatalytic performance was a result of an efficient migration of excited electrons from BiOBr to MoS2, prolonging the electron-hole pairs recombination rate. A possible charge transfer diagram of this hybrid composite photocatalyst, and the reaction mechanism for the photodegradation of RB5 were proposed.