Upconversion nanoparticles coupled with hierarchical ZnIn2S4 nanorods as a near-infrared responsive photocatalyst for photocatalytic CO2 reduction

Full-Spectrum Utilization of ZIF-67/Ag NPs/NaYF4:Yb,Er Photocatalysts for Efficient Degradation of Sulfadiazine: Upconversion Mechanism and DFT Calculation

In this work, novel ternary composite ZIF-67/Ag NPs/NaYF4:Yb,Er is synthesized by solvothermal method. The photocatalytic activity of the composite is evaluated by sulfadiazine (SDZ) degradation under simulated sunlight. High elimination efficiency of the composite is 95.4% in 180 min with good reusability and stability. The active species (h+, ·O2 - and ·OH) are identified. The attack sites and degradation process of SDZ are deeply investigated based on theoretical calculation and liquid chromatography-mass spectrometry analysis. The upconversion mechanism study shows that favorable photocatalytic effectiveness is attributed to the full utilization of sunlight through the energy transfer upconversion process and fluorescence resonance energy transfer. Additionally, the composite is endowed with outstanding light-absorbing qualities and effective photogenerated electron-hole pair separation thanks to the localized surface plasmon resonance effect of Ag nanoparticles. This work can motivate further design of novel photocatalysts with upconversion luminescence performance, which are applied to the removal of sulphonamide antibiotics in the environment.

CO2 Enrichment Boosts Highly Selective Infrared-Light-Driven CO2 Conversion to CH4 by UiO-66/Co9S8 Photocatalyst

Photocatalytic CO2 reduction to high-value chemicals is an attractive approach to mitigate climate change, but it remains a great challenge to produce a specific product selectively by IR light. Hence, UiO-66/Co9S8 composite is designed to couple the advantages of metallic photocatalysts and porous CO2 adsorbers for IR-light-driven CO2-to-CH4 conversion. The metallic nature of Co9S8 endows UiO-66/Co9S8 with exceptional IR light absorption, while UiO-66 dramatically enhances its local CO2 concentration, revealed by finite-element method simulations. As a result, Co9S8 or UiO-66 alone does not show observable IR-light photocatalytic activity, whereas UiO-66/Co9S8 exhibits exceptional activity. The CH4 evolution rate over UiO-66/Co9S8 reaches 25.7 µmol g-1 h-1 with ca.100% selectivity under IR light irradiation, outperforming most reported catalysts under similar reaction conditions. The X-ray absorption fine structure spectroscopy spectra verify the presence of two distinct Co sites and confirm the existence of metallic Co─Co bond in Co9S8. Energy diagrams analysis and transient absorption spectra manifest that CO2 reduction mainly occurs on Co9S8 for UiO-66/Co9S8, while density functional theory calculations demonstrate that high-electron-density Co1 sites are the key active sites, possessing lower energy barriers for further protonation of *CO, leading to the ultra-high selectivity toward CH4.

Enhancement of Charge Separation and NIR Light Harvesting through Construction of 2D-2D Bi4 O5 I2 /BiOBr:Yb3+ , Er3+ Z-Scheme Heterojunctions for Improved Full-Spectrum Photocatalytic Performance

Developing full-spectrum photocatalysts with simultaneous broadband light absorption, excellent charge separation, and high redox capabilities is becoming increasingly significant. Herein, inspired by the similarities in crystalline structures and compositions, a unique 2D-2D Bi₄ O₅ I₂ /BiOBr:Yb³⁺ ,Er³⁺ (BI-BYE) Z-scheme heterojunction with upconversion (UC) functionality is successfully designed and fabricated. The co-doped Yb³⁺ and Er³⁺ harvest near-infrared (NIR) light and then convert it into visible light via the UC function, expanding the optical response range of the photocatalytic system. The intimate 2D-2D interface contact provides more charge migration channels and enhances the Förster resonant energy transfer of BI-BYE, leading to significantly improved NIR light utilization efficiency. Density functional theory (DFT) calculations and experimental results confirm that the Z-scheme heterojunction is formed and that this heterojunction endows the BI-BYE heterostructure with high charge separation and strong redox capability. Benefit from these synergies, the optimized 75BI-25BYE heterostructure exhibits the highest photocatalytic performance for Bisphenol A (BPA) degradation under full-spectrum and NIR light irradiation, outperforming BYE by 6.0 and 5.3 times, respectively. This work paves an effective approach for designing highly efficient full-spectrum responsive Z-scheme heterojunction photocatalysts with UC function.

Achieving improved full-spectrum responsive 0D/3D CuWO4/BiOBr:Yb3+,Er3+ photocatalyst with synergetic effects of up-conversion, photothermal effect and direct Z-scheme heterojunction

The key to obtain effective photocatalysts is to increase the efficiency of light energy conversion, and thus the design and implementation of full-spectrum photocatalysts is a potential approach to solve this problem especially by extending the absorption range to near-infrared (NIR) light. Herein, the improved full-spectrum responsive CuWO₄/BiOBr:Yb³⁺,Er³⁺ (CW/BYE) direct Z-scheme heterojunction was prepared. The CW/BYE with CW mass ratio of 5% had the best degradation performance, and the removal rate of tetracycline reached 93.9% in 60 min and 69.4% in 12 h under visible (Vis) and NIR light, respectively, which were 5.2 and 3.3 times of BYE. According to the outcome of experimental, the reasonable mechanism of improved photoactivity was put forward on the basis of (i) the up-conversion (UC) effect of Er³⁺ ion to convert NIR photon to ultraviolet or visible light, which can be used by CW and BYE, (ii) the photothermal effect of CW to absorb the NIR light, increasing the local temperature of photocatalyst particle to accelerate the photoreaction, and (iii) the formed direct Z-scheme heterojunction between BYE and CW to boost the separation of photogenerated electron-hole pairs. Additionally, the excellent photostability of the photocatalyst was verified by cycle degradation experiments. This work opens up a promising technique for designing and synthesizing full-spectrum photocatalysts by utilizing synergetic effects of UC, photothermal effect and direct Z-scheme heterojunction.

Hydroxyl-modified Nb4C3Tx MXene@ZnIn2S4 sandwich structure for photocatalytic overall water splitting

Herein, a hydroxyl-modified MXene@ZnIn₂S₄ (Nb₄C₃T_x MXene@ZIS-OH) overall water splitting photocatalyst with a sandwich structure was prepared through an in-situ growth strategy and peroxyl plasma post-treatment. The Nb₄C₃T_x MXene@ZIS-OH exhibits outstanding catalytic performance, which generates the release rates of hydrogen (53.8 μmol g^-1h^-1) and oxygen (26.7 μmol g^-1h^-1) from the water under visible light irradiation. After four photocatalytic cycling, the photocatalytic overall water splitting activity of Nb₄C₃T_x MXene@ZIS-OH is still 95.9% of the initial activity, which indicates that Nb₄C₃T_x MXene@ZIS-OH exhibits excellent cycling stability. Notably, the Nb₄C₃T_x MXene@ZIS-OH achieves an AQY of 1.2% for the overall photocatalytic water splitting at 380 nm. The sandwich structure and matched heterointerface between high work function Nb₄C₃T_x MXene and ZnIn₂S₄ nanosheets promote the electron transport, inhibit the charge recombination, and separate the generated H₂ and O₂ with effectiveness. Importantly, the Finite-Difference Time-Domain (FDTD) simulation suggests the hydroxyl groups on the surface of ZnIn₂S₄ could increase the hydrophilicity of photocatalyst and capture the holes generated by photoexcitation, thereby promoting the separation of electron-hole pairs rapidly. This work presents a successful example of constructing overall water splitting photocatalysts by energy level regulation, structure design and functional group modification.

Synergetic control of specific orientation and self-distribution of photoelectrons in micro-nano ZnIn2S4/black phosphorus quantum dots (BPQDs) heterojunction to enhance photocatalytic hydrogen evolution

Black phosphorus quantum dots (BPQDs)-based materials possess excellent photocatalytic efficiency; however, they often present a loss of photo-induced carriers and random active sites in electron transfer of heterojunctions, thus restricting the enhancement of hydrogen (H₂) evolution and their potential application. In this study, a micro-nano ZnIn₂S₄/BPQDs (MN-ZISBP) composite is constructed to enable specific orientation and self-distribution of photoelectrons transferred from ZnIn₂S₄ (ZIS) to BPQDs. The relationship between photoelectron transfer and H₂ evolution efficiency is investigated via experiments and density functional theory (DFT) calculations. MN-ZISBP with a nanorod-like structure presents an H₂ evolution rate of 1207 μmol/g/h and is higher than that of the sheet-shaped (S-ZISBP, 1023 μmol/g/h) and flower-like composites (F-ZISBP, 744 μmol/g/h) under visible light irradiation. The MN-ZISBP composite with a lower conduction band level and larger specific surface area increases the number of active sites on BPQDs via "self-distribution" for H₂ evolution. Finally, the electron transfer direction and bonding orbitals of MN-ZISBP are calculated using the work function and density of states results to verify the above conclusions. The novel construction technique and photocatalytic mechanism of MN-ZISBP reported in this study provide significant insights into the BPQDs-based photocatalysts for H₂ evolution.

Near-Infrared Light Driven ZnIn2S4-Based Photocatalysts for Environmental and Energy Applications: Progress and Perspectives

Zinc indium sulfide (ZnIn₂S₄), as a significant visible-light-responsive photocatalyst, has become a research hotspot to tackle energy demand and environmental issues owing to its excellent properties of high stability, easy fabrication, and remarkable catalytic activity. However, its drawbacks, including low utilization of solar light and fast photoinduced charge carriers, limit its applications. Promoting the response for near-infrared (NIR) light (~52% solar light) of ZnIn₂S₄-based photocatalysts is the primary challenge to overcome. In this review, various modulation strategies of ZnIn₂S₄ have been described, which include hybrid with narrow optical gap materials, bandgap engineering, up-conversion materials, and surface plasmon materials for enhanced NIR photocatalytic performance in the applications of hydrogen evolution, pollutants purification, and CO₂ reduction. In addition, the synthesis methods and mechanisms of NIR light-driven ZnIn₂S₄-based photocatalysts are summarized. Finally, this review presents perspectives for future development of efficient NIR photon conversion of ZnIn₂S₄-based photocatalysts.

Novel La3+/Sm3+ co-doped Bi5O7I with efficient visible-light photocatalytic activity for advanced treatment of wastewater: Internal mechanism, TC degradation pathway, and toxicity analysis

Controlling semiconductor photocatalysts by doping rare-earth ions is an effective strategy to improve photocatalytic performance. Simple solvothermal and calcination methods were used to prepare La³⁺ and Sm³⁺ modified Bi₅O₇I nanomaterials. Some characterizations such as XRD, XPS, SEM, TEM, UV-vis, etc. were carried out to explore its structural composition and photoelectrochemical properties. The photocatalytic activity was investigated by simulating the degradation of TC and RhB under visible-light irradiation. The degradation results showed that the photocatalytic efficiency of 4S4L-Bi₅O₇I was the best among the samples with the 100% degradation rate of TC (Tetracycline hydrochloride) and 93% of RhB (Rhodamine B). The capture experiment and ESR test proved that the active substances that play a role in the photocatalytic degradation of pollutants were ·O₂^-, ¹O₂ and h⁺, and on this basis, the possible degradation mechanism was proposed. The final results showed that La/Sm co-doping expanded the light absorption range of Bi₅O₇I and improved the charge separation efficiency and the specific surface area. Besides, the surface defects were formed on the surface of Bi₅O₇I due to ion-doping, which could catch e^- to promote the separation and transfer of carriers and improve the photocatalytic activity. LC-MS was used to analyze the possible degradation pathways of TC. And the toxicity of TC was also analyzed via T.E.S.T and Toxtree. The results showed comprehensive toxicity of TC was decreased by 4S4L-Bi₅O₇I so that the overall water pollution was reduced. This work can provide a reference for the subsequent development of bismuth-based photocatalysts.

Cobalt quantum dots as electron collectors in ultra-narrow bandgap dioxin linked covalent organic frameworks for boosting photocatalytic solar-to-fuel conversion

Photocatalysis offers a sustainable paradigm for solar-to-fuel conversion because it conflates the merits of renewable solar energy and reusable catalysts. However, the seek for robust photocatalysts that can utilize the full visible light spectrum remains challenging. Herein, cobalt quantum dots (Co QDs) were integrated into ultra-narrow bandgap dioxin linked covalent organic frameworks (COF-318) for photocatalytic solar-to-fuel conversion under full spectrum of visible light irradiation. The optimal Co₁₀-COF exhibited superior photocatalytic CO₂ reduction performance, affording a CO yield of 4232 µmol∙g^-1∙h^-1 and H₂ evolution of 6611 µmol∙g^-1∙h^-1. Specifically, Co QDs played a crucial role in boosting the photocatalytic performance, which acted as electron collectors to capture the photoinduced electrons and then conveyed them to CO₂ molecules. Moreover, the Co QDs modification significantly improved the CO₂ adsorption and activation capacity, as well as prolonging the lifetime of photogenerated carriers. This work reveals an operable pathway for fabricating promising photocatalyst for visible-light-driven solar-to-fuel generation and provides insight into the impact of the integration of Co QDs on COF-based photocatalysts.

The Potential Strategies of ZnIn2S4-Based Photocatalysts for the Enhanced Hydrogen Evolution Reaction

Photocatalysis is a potential strategy to solve energy and environmental problems. The development of new sustainable photocatalysts is a current topic in the field of photocatalysis. ZnIn2S4, a visible light-responsive photocatalyst, has attracted extensive research interest in recent years. Due to its suitable band gap, strong chemical stability, durability, and easy synthesis, it is expected to become a new hot spot in the field of photocatalysis in the near future. This mini-review presents a comprehensive summary of the modulation strategies to effectively improve the photocatalytic activity of ZnIn2S4 such as morphology and structural engineering, defects engineering, doping engineering, and heterojunction engineering. This review aims to provide reference to the proof-of-concept design of highly active ZnIn2S4-based photocatalysts for the enhanced hydrogen evolution reaction.

Monochromatic light-enhanced photocatalytic CO2 reduction based on exciton properties of two-dimensional lead halide perovskites

Converting CO₂ into valuable solar fuels through photocatalysis has been considered a green and sustainable technology that is promising for alleviating global warming and providing energy in an environmentally friendly manner. However, traditional photocatalysts generally suffer from low surface-reactive reaction sites, inefficient light harvesting and rapid recombination of electron-hole pairs. Lead halide perovskite materials have been considered ideal semiconductor photocatalysts for photocatalytic CO₂ reduction due to their tunable band gaps, strong light absorption, and low cost. Herein, a series of L₂Cs_n-1Pb_nX_3n+1 (L = ba, ha, oa; X = Cl, Br, I; n = 1, 2) 2D layered perovskites were synthesized by a facile solvothermal method. The effects of alkyl amine chain length, halogen atoms and inorganic layer number on their properties were studied. More importantly, these 2D materials were used as photocatalysts for CO₂ reduction without any sacrificial agents. These 2D perovskites exhibited markedly increased performance in comparison with 3D bulk materials, benefitting from the larger surface-area-to-volume ratio and faster and more efficient exciton dissociation, which achieved the highest CO yield of 158.69 μmol g^-1 h^-1 and CH₄ yield of 6.9 μmol g^-1 h^-1 through the design of the photocatalytic system. In addition, the influence of light source conditions on photocatalysis was studied systematically, including light source intensity and wavelength. The experimental results indicated that an appropriate solvent, high light intensity and monochromatic light source matching the wavelength of exciton absorption can effectively improve the photocatalytic efficiency.