Switching charge transfer process of carbon nitride and bismuth vanadate by anchoring silver nanoparticle toward cocatalyst free water reduction

Design and application of g-C3N4-based materials for fuels photosynthesis from CO2 or H2O based on reaction pathway insights

Photocatalytic CO2 reduction reaction (CRR) and hydrogen evolution reaction (HER) based on graphitic carbon nitride (g-C3N4) that is regarded as the metal-free "holy grail" photocatalyst, provide promising strategies for producing next-generation fuels, contributing to achieving carbon neutrality, alleviating energy and environment crisis. However, the activity of CRR and HER over g-C3N4 leaves much to be desired. Therefore, numerous studies have sprung up to enhance photoactivity. A comprehensive understanding of the CRR and HER reaction pathways is crucial for designing g-C3N4-based materials, further promoting efficient fuel production. Different from previous reviews that focus on g-C3N4 modification from the viewpoint of material science. In this review, we divided the multistep processes of CRR and HER into five reaction pathways and summarized the latest advances for improving each pathway of fuels synthesis through CRR or HER. Meanwhile, the existing bottleneck issues of each step were also discussed. Finally, comprehensive conclusions, including the remaining challenges, outlooks, etc., for CRR and HER over g-C3N4 were put forward. We are sure that this review will conduce to the understanding of the structure-activity relationship between CRR, HER processes, and g-C3N4 structure, which can provide the reference for developing high-powered photocatalysts, not confined to g-C3N4.

Silver nanoparticles embedded 2D g-C3N4nanosheets toward excellent photocatalytic hydrogen evolution under visible light

Photocatalytic water splitting is considered to be a feasible method to replace traditional energy. However, most of the catalysts have unsatisfactory performance. In this work, we used a hydrothermal process to grow Ag nanoparticlesin situon g-C₃N₄nanosheets, and then a high performance catalyst (Ag-g-C₃N₄) under visible light was obtained. The Ag nanoparticles obtained by this process are amorphous and exhibit excellent catalytic activity. At the same time, the local plasmon resonance effect of Ag can effectively enhance the absorption intensity of visible light by the catalyst. The hydrogen production rate promote to 1035μmol g^-1h^-1after loaded 0.6 wt% of Ag under the visible light, which was 313 times higher than that of pure g-C₃N₄(3.3μmol g^-1h^-1). This hydrogen production rate is higher than most previously reported catalysts which loaded with Ag or Pt. The excellent activity of Ag-g-C₃N₄is benefited from the Ag nanoparticles and special interaction in each other. Through various analysis and characterization methods, it is shown that the synergy between Ag and g-C₃N₄can effectively promote the separation of carriers and the transfer of electrons. Our work proves that Ag-g-C₃N₄is a promising catalyst to make full use of solar energy.

Enhanced photocatalytic activity of Bi2WO6 with PVP addition for CO2 reduction into ethanol under visible light

The conversion of CO₂ into new carbon-based products, such as fuels and chemicals, is an attractive and promising means of mitigating global energy needs and minimizing environmental damage. Although bismuth tungstate (Bi₂WO₆) as a photocatalyst can promote CO₂ photoreduction, a systematic study for the development of a low-cost and efficient catalyst is needed. Thus, Bi₂WO₆ with different morphologies was successfully synthesized using the hydrothermal method. An experimental design was applied to investigate the effect of synthesis time and PVP (polyvinylpyrrolidone) concentration on catalyst photocatalytic activity. Crystal structures, morphologies, optical absorption, and surface charges of the catalysts were characterized by X-ray diffraction, scanning electron microscope, UV-vis diffuse-reflection spectroscopy, nitrogen adsorption, and zeta potential. All samples exhibited good performance for the photoreduction of CO₂ into ethanol, and both time and PVP concentration were significant in the ethanol yield. Changes in synthesis conditions induced differences in catalyst characteristics, such as morphology, crystallinity, and, predominantly, surface area. Furthermore, PVP addition improved photocatalytic efficiency by up to 258% compared with results without the surfactant. The best sample, W-8h-10%, presented a flower-like morphology and ethanol yield of 68.9 μmol g^-1 h^-1.

S-scheme bismuth vanadate and carbon nitride integrating with dual-functional bismuth nanoparticles toward co-efficiently removal formaldehyde under full spectrum light

It is crucial to develop more effective photocatalysts in the field of clean environment. In response, the S-scheme BiVO₄/g-C₃N₄ heterojunction modified by in situ reduced non-noble metal Bi nanoparticles was used to synergistically degrade formaldehyde under full spectral irradiation. The results, that investigated by careful characterizations and density functional theory (DFT) calculations, proved that BiVO₄/g-C₃N₄ form an S-scheme heterojunction, which can effectively improve the separation efficiency of photogenic carriers and maintain the original strong redox capability of semiconductor materials. The SPR effect of Bi elemental substance enhanced the optical response and provided more oxidative species. Thus, the photocatalytic activity of BiVO₄/Bi/g-C₃N₄ was significantly improved through their joint efforts, that the degradation efficiency of HCHO (800 ppm) for 6 h is 96.39% under 300 W Xenon lamp without filter with the pseudo-second-order rate constant of 4.16 ppm^-1·h^-1 and CO₂ selectivity of 98.41%. Surprisingly, the degradation efficiency also reached to 49.35% and 32.23% under visible and near-infrared light irradiation, respectively. Moreover, we also tested its photocatalytic decomposition effect on formaldehyde in coatings, indicating that it has a broad prospect in future coatings applications. This study may provide an expected photocatalyst, an efficient non-noble metal modified S-scheme heterojunction, to degrade volatile organic gases under a broad spectrum light.

Fabrication of ultra-sensitive photoelectrochemical aptamer biosensor: Based on semiconductor/DNA interfacial multifunctional reconciliation via 2D-C3N4

In this work, we fabricate a novel bismuth vanadate/two dimensional-carbon nitride/deoxyribonucleic acid (BiVO₄/2D-C₃N₄/DNA) aptamer photoelectrochemical (PEC) sensor, and this sensor provides a record detection sensitivity area (5 × 10^-7 μg/L - 10 μg/L) for Microcystin-LR (MC-LR). Meanwhile, except for MC-LR detection, this sensor presents highly sensitivity for tumor marker, heavy metal ion, antibiotic also by changing the DNA aptamer. Photo charge dynamic and theory calculation results reveal that 2D-C₃N₄ is a key material for multifunctional interface reconciliation of this PEC aptamer sensor. Firstly, it can serve as photogenerated hole oriented-transfer medium from the BiVO₄ photoanode to the detective target; In addition, 2D-C₃N₄ with large area of π electron cloud can fix the DNA aptamer parallelly by π-π bonding with the nucleic acid in the DNA aptamer to shorten the hole transfer distance from the semiconductor to target. So that, a record MC-LR detection sensitivity has been achieved by the 2D-C₃N₄ modified BiVO₄/DNA aptamer sensor.

Enhanced photocatalytic activity of Ag/Ag2Ta4O11/g-C3N4 under wide-spectrum-light irradiation: H2 evolution from water reduction without co-catalyst

Designing a superior and stable catalyst toward H₂ evolution under solar light to solve the energy crisis has attracted wide concern. Herein, we have constructed a novel heterojunction photocatalyst Ag/Ag₂Ta₄O₁₁/g-C₃N₄ by in situ assembly, which can efficiently split water to generate H₂ by utilizing wide-spectrum-light irradiation. Optimal H₂ production reaches highly to 253.03 μmol g^-1 h^-1 under the simulated solar light. Moreover, the catalyst presented well stability by the retained 98% photocatalytic activity and invariable textural structure after five recycling tests. The mechanism of H₂ generation over the prepared material was carefully investigated through scanning electron microscope (SEM), transmission electron microscopy (TEM), UV-Vis absorption spectra (UV-Vis), photoluminescence analysis (PL), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR), and several electrochemical measurements. It is proposed that the carriers are efficiently separated through Ag-mediated Z-scheme route in space, retaining their strong redox ability. Ag particles produced by in situ reduction from the component Ag₂Ta₄O₁₁ could devote to the quick electron migration as the bridge center, effective solar light harvesting due to their surface plasmon resonance, and excellent stability by inhibiting their agglomeration and elution. This research offers a new idea for constructing full solid Z-scheme photocatalysts under wide-spectrum-light irradiation.

Unraveling the impact of the Pd nanoparticle@BiVO4/S-CN heterostructure on the photo-physical & opto-electronic properties for enhanced catalytic activity in water splitting and one-pot three-step tandem reaction

Herein, a Pd nanoparticle-embedded SBVCN-37 heterostructure photocatalyst was synthesized and employed in the water-splitting reaction and for the synthesis of imines via a one-pot tandem reaction involving the photocatalytic reduction of nitrobenzene and oxidation of benzyl alcohol, followed by their condensation reaction. The embedded Pd nanoparticles (mean diameter ∼ 5-7 nm) act as an electron mediator and enhance the catalytic activity of SBVCN-37 during the oxidation and reduction reactions. The experimental results confirm that the light-induced holes owing to the favourable redox potential of the catalyst oxidize N₂H₄ to N₂ and liberate H⁺ ions, which subsequently react with photogenerated electrons to facilitate the reduction of nitrobenzene. The obtained quantum yields for benzyl alcohol oxidation and nitrobenzene reduction were calculated to be 2.08% and 6.53% at λ = 420 nm light illumination, respectively. Furthermore, the obtained apparent quantum yields for the OER and HER were calculated to be 10.22% and 12.72% at 420 nm, respectively, indicating the excellent potential of the investigated photocatalyst for solar fuel production. Photoelectrochemical (PEC) and time-resolved and steady-state photoluminescence measurements reveal that the optimum amount of Pd nanoparticles over SBVCN-37 is the crucial factor for achieving the highest photocurrent response, lowest charge transfer resistance, and efficient carrier mobility, leading to prominent catalytic activity. Furthermore, the Mott-Schottky (M-S) analysis confirmed that the deposition of Pd nanoparticles effectively reduced the over-potential and fine-tuned the band edge potential required for the HER and OER reactions, respectively.

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles

A novel heterostructured nanocomposite UCNPs@SiO₂@Ag/g-C₃N₄ was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C₃N₄. Its photocatalytic properties and photocatalytic mechanism were investigated. The as-synthesized photocatalyst with excellent improvement in the solar absorption and separation efficiency of photoinduced electron–hole pairs exhibited optimum solar-induced photocatalytic activity in dye degradation and hydrogen production. The experimental results showed that the rates of degradation of Rhodamine B (RhB) and hydrogen evolution were about 10 and 12 times higher than that of pristine g-C₃N₄, respectively. The excellent photocatalytic activity was attributed to the synergetic effect of upconversion nanoparticles (UCNPs) and Ag nanoparticles (NPs) on the modification of the photocatalytic properties of g-C₃N₄, resulting in a broad light response range for g-C₃N₄ as well as the fast separation and slow recombination of photoinduced electron–hole pairs. This study provides new insight into the fabrication of g-C₃N₄-based nanocomposite photocatalysts with high catalytic efficiency through the artful assembly of UCNPs, Ag NPs and g-C₃N₄ into a hetero-composite nanostructure. The prominent improvement in photocatalytic activity enables the potential application of g-C₃N₄ in the photocatalytic degradation of organic pollutants and hydrogen production utilizing solar energy.

A novel heterostructured nanocomposite UCNPs@SiO₂@Ag/g-C₃N₄ was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C₃N₄.