Multicomponent hydroxides supported Cu/Cu2O nanoparticles for high efficient photocatalytic ammonia synthesis

Cu-based S-scheme photocatalysts

S-scheme heterojunctions have become a hot topic in photocatalysis. Copper (Cu) compounds are a versatile family of photocatalytic materials, including oxides (CuO, Cu2O), binary oxides (CuBi2O4, CuFe2O4), sulfides (CuxS, (1 ≤ x ≤ 2)), selenides (CuSe), phosphides (Cu3P), metal organic frameworks (MOFs), etc. These materials are characterized by narrow bandgaps, large absorption coefficients, and suitable band positions. To further increase the efficiency of photoinduced charge separation, Cu-based photocatalytic materials are widely integrated into S-scheme heterojunctions and exploited for the hydrogen evolution reaction (HER), CO2 reduction, H2O2 generation, N2 fixation, and pollutant degradation. This review comprehensively discusses recent progress in Cu-based S-scheme heterojunctions, and highlights their considerable potential for targeted applications in sustainable energy conversion, environmental remediation, and beyond. The fundamentals of S-scheme charge transfer, the design principles and verification tools are summarized. Then, the review describes the Cu-based photocatalytic materials, categorized according to their chemical composition, and their integration in S-scheme heterojunctions for photocatalytic applications. In particular, the implications of the S-scheme charge transfer mechanism on promoting the catalytic activity of selected systems are analyzed. Finally, current limitations and outlooks are provided to motivate future studies on developing novel and advanced Cu-based S-scheme photocatalysts with high performance and studying the underlying photocatalytic mechanisms.

Low-Crystallized Carbon as an Electron Mediator in g-C3N4/C/TiO2 for Enhancing Photocatalytic Degradation of Antibiotics

Photodegradation of antibiotics based on photocatalytic semiconductors is a promising option to alleviate water pollution. Despite its limitations, TiO2-based photocatalysts are still the most widely studied materials for pollutant degradation. In this work, a pomegranate-like g-C3N4/C/TiO2 nano-heterojunction was constructed using the hydrothermal-calcination method, consisting of interconnected small crystals with a dense structure and closely contacted interface. Low-crystallized carbon filled the gap between TiO2 and g-C3N4, forming a large interface. The local in-plane heterostructures generated by C/g-C3N4 are further improved for carrier transport. As expected, the optimal sample calcined at 300 °C (GTC-300) efficiently eliminated tetracycline hydrochloride (TC-HCl, 20 mg L-1), achieving a removal rate of up to 92.9% within 40 min under full-spectrum irradiation and 87.8% within 60 min under the visible spectrum (λ > 400 nm). The electron mediator, low-crystallized carbon, successfully promoted the formation of new internal electric fields via the widespread heterojunction interface, which accelerated the separation and migration of photogenerated carriers between g-C3N4 and TiO2. These results confirm that the g-C3N4/C/TiO2 nano-heterojunction exhibited outstanding photodegradation performance of TC-HCl. The electron mediator shows great potential in promoting carrier transfer and enhancing photocatalytic performance of heterogeneous photocatalysts in water treatment.

Unveiling the potential of step-scheme and Type II photocatalysts in dinitrogen reduction to ammonia

Innovative photocatalytic systems designed to enhance efficiency of nitrogen fixation processes, specifically focusing on sustainable ammonia (NH3) production strategies via dinitrogen (N2) reduction into ammonia (NH3). This process is critical for sustainable agriculture and energy production. To improve photocatalyst activity, catalyst stability and reusability, reduction efficiency due to electron/hole recombination, and light-absorption efficiency has drawn extensive attention. Herein, a broad range of research progress and comprehensive overview of step-scheme/type-II heterojunctions focusing on dinitrogen (N2) reduction are reviewed with focus on general synthesis, characterization by their unique charge separation mechanisms that improve light absorption and electron-hole pair utilization. The review highlights recent advancements in material design, which have shown promising results in enhancing photocatalytic activity under visible light irradiation. A significant portion of the review delves into the underlying mechanisms which these heterojunctions operate. Despite the promising literature results, several challenges facing this field, such as scalability, stability of photocatalysts, and environmental impact under operational conditions were also discussed. In summary, this review provides valuable insights into the potential of step-scheme/type-II photocatalysts for dinitrogen reduction to ammonia. The need for interdisciplinary approaches to overcome existing challenges such as incorporation of piezoelectric biomaterials and unlocking the full potential of these materials in addressing global nitrogen demands sustainably are highlighted, outlining future directions for further research and innovations.

Modulating band structure through introducing Cu0/CuxO composites for the improved visible light driven ammonia synthesis

The photocatalytic performance of ceria-based materials can be tuned by adjusting the surface structures with decorating the transition-metal, which are considered as the important active sites. Herein, cuprous oxide-metallic copper composite-doped ceria nanorods were assembled through a simple hydrothermal reduction method. The photocatalytic ammonia synthesis rates exhibit an inverted "V-shaped" trend with increasing Cu0/CuxO mole ratio. The best ammonia production rate, approximately 900 or 521 µmol·gcal-1·h-1 under full-spectra or visible light, can be achieved when the Cu0/CuxO ratio is approximately 0.16, and this value is 8 times greater than that of the original sample. The absorption edge of the as-prepared samples shifted towards visible wavelengths, and they also had appropriate ammonia synthesis levels. This research provides a strategy for designing noble metal-free photocatalysts through introducing the metal/metallic oxide compositesto the catalysts.

Fabrication of Ultrafine Cu2 O Nanoparticles on W18 O49 Ultra-Thin Nanowires by In-Situ Reduction for Highly Efficient Photocatalytic Nitrogen Fixation

Photocatalytic ammonia synthesis technology is one of the important methods to achieve green ammonia synthesis. Herein, two samples of Cu ion-doped W18 O49 with different morphologies, ultra-thin nanowires (Cu-W18 O49 -x UTNW) and sea urchin-like microspheres (Cu-W18 O49 -x SUMS), are synthesized by a simple solvothermal method. Subsequently, Cu2 O-W18 O49 -x UTNW/SUMS is synthesized by in situ reduction, where the NH3 production rate of Cu2 O-W18 O49 -30 UTNW is 252.4 µmol g-1  h-1 without sacrificial reagents, which is 11.8 times higher than that of the pristine W18 O49 UTNW. The Cu2 O-W18 O49 -30 UTNW sample is rich in oxygen vacancies, which promotes the chemisorption and activation of N2 molecules and makes the N≡N bond easier to dissociate by proton coupling. In addition, the in situ reduction-generated Cu2 O nanoparticles exhibit ideal S-scheme heterojunctions with W18 O49 UTNW, which enhances the internal electric field strength and improves the separation and transfer efficiency of the photogenerated carriers. Therefore, this study provides a new idea for the design of efficient nitrogen fixation photocatalysis.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 μ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.