Highly efficient and stable Ag/AgIO₃ particles for photocatalytic reduction of CO₂ under visible light

Oxygen-deficient AgIO3 for efficiently photodegrading organic contaminants under natural sunlight

Defect engineering is regarded as an effective strategy to boost the photo-activity of photocatalysts for organic contaminants removal. In this work, abundant surface oxygen vacancies (Ov) are created on AgIO3 microsheets (AgIO3-OV) by a facile and controllable hydrogen chemical reduction approach. The introduction of surface Ov on AgIO3 broadens the photo-absorption region from ultraviolet to visible light, accelerates the photoinduced charges separation and migration, and also activates the formation of superoxide radicals (•O2-). The AgIO3-OV possesses an outstanding degradation rate constant of 0.035 min-1, for photocatalytic degrading methyl orange (MO) under illumination of natural sunlight with a light intensity is 50 mW/cm2, which is 7 and 3.5 times that of the pristine AgIO3 and C-AgIO3 (AgIO3 is calcined in air without generating Ov). In addition, the AgIO3-OV also exhibit considerable photoactivity for degrading other diverse organic contaminants, including azo dye (rhodamine B (RhB)), antibiotics (sulflsoxazole (SOX), norfloxacin (NOR), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)), and even the mixture of organic contaminants (MO-RhB and CTC-OFX). After natural sunlight illumination for 50 min, 41.4% of total organic carbon (TOC) for MO-RhB mixed solution can be decreased over AgIO3-OV. In a broad range of solution pH from 3 to 11 or diverse water bodies of MO solution, AgIO3-OV exhibits attractive activity for decomposing MO. The MO photo-degradation process and mechanism over AgIO3-OV under natural sunlight irradiation has been systemically investigated and proposed. The toxicities of MO and its degradation intermediates over AgIO3-OV are compared using Toxicity Estimation Software (T.E.S.T.). Moreover, the non-toxicity of both AgIO3-OV catalyst and treated antibiotic solution (CTC-OFX mixture) are confirmed by E. coli DH5a cultivation test, supporting the feasibility of AgIO3-OV catalyst to treat organic contaminants in real water under natural sunlight illumination.

Recent Trends in Plasmon-Assisted Photocatalytic CO2 Reduction

Direct photocatalytic reduction of CO₂ has become an highly active field of research. It is thus of utmost importance to maintain an overview of the various materials used to sustain this process, find common trends, and, in this way, eventually improve the current conversions and selectivities. In particular, CO₂ photoreduction using plasmonic photocatalysts under solar light has gained tremendous attention, and a wide variety of materials has been developed to reduce CO₂ towards more practical gases or liquid fuels (CH₄ , CO, CH₃ OH/CH₃ CH₂ OH) in this manner. This Review therefore aims at providing insights in current developments of photocatalysts consisting of only plasmonic nanoparticles and semiconductor materials. By classifying recent studies based on product selectivity, this Review aims to unravel common trends that can provide effective information on ways to improve the photoreduction yield or possible means to shift the selectivity towards desired products, thus generating new ideas for the way forward.

Composite of α-FeOOH and Mesoporous Carbon Derived from Indian Blackberry Seeds as Low-Cost and Recyclable Photocatalyst for Degradation of Ciprofloxacin

This study aims to analyse the use of biowaste-derived carbon in enhancing the photocatalytic effect of Earth-abundant visible light active goethite (α−FeOOH). The biowaste material used in this case is seeds of the Indian blackberry fruit. The FeOOH/C composite has been synthesized using an assisted sonochemical technique. The photocatalysts have been characterized using powder x-ray diffraction, nitrogen adsorption isotherms and scanning electron microscopy technique. FTIR and Raman studies have been carried out to understand the structure bonding correlation. The band gap has been ascertained using Tauc plots. The adsorption and consequent photodegradation of CIP have been studied via UV-visible spectroscopy and the mechanism has been ascertained by using radical quenching techniques. The charge separation efficiency has been ascertained through photoluminescence (PL) studies and electrochemical impedance studies (EIS). The pivotal role played by photogenerated holes (h+) in the photocatalytic degradation of CIP has been highlighted. The low cost biowaste-derived carbon as a constituent of the FeOOH/C composite shows great promise as a supporting material for enhancing the photocatalytic properties of such semiconductor materials.

Construction of BiOIO3/AgIO3 Z-Scheme Photocatalysts for the Efficient Removal of Persistent Organic Pollutants under Natural Sunlight Illumination

The efficient removal of persistent organic pollutants (POPs) in natural waters is vital for human survival and sustainable development. Photocatalytic degradation is a feasible and cost-effective strategy to completely disintegrate POPs at room temperature. Herein, we develop a series of direct Z-scheme BiOIO₃/AgIO₃ hybrid photocatalysts via a facile deposition-precipitation method. Under natural sunlight irradiation, the light intensity of which is ∼40 mW/cm², a considerable rate constant of 0.185 min^-1 for photodecomposing 40 mg/L MO is obtained over 0.5 g/L Bi@Ag-5 composite photocatalyst powder, about 92.5 and 5.3 times higher than those of pristine AgIO₃ and BiOIO₃. The photoactivity of Bi@Ag-5 for photodecomposing MO under natural sunlight illumination surpasses most of the reported photocatalysts under Xe lamp illumination. After natural sunlight irradiation for 20 min, 95% of MO, 82% of phenol, 78% of 2,4-DCP, 54% of ofloxacin, and 88% of tetracycline hydrochloride can be photodecomposed over Bi@Ag-5. Relative to the commercial photocatalyst TiO₂ (P25), Bi@Ag-5 exhibits greatly higher photoactivity for the treatment of MO-phenol-tetracycline hydrochloride mixture pollutants in the scale-up experiment of 500 mL of solution, decreasing COD, TOC, and chromaticity value by 52, 19, and 76%, respectively, after natural sunlight irradiation for 40 min. The photodegradation process and mechanism of MO have been systematically investigated and proposed. This work provides an archetype for designing efficient photocatalysts to remove POPs.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction

The photocatalytic CO₂ reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In₂O₃ plasmonic photocatalysts. The Ag-In₂O₃ compounds show remarkedly enhanced photocatalytic activity for CO₂ conversion to CO compared to pristine In₂O₃. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag-In₂O₃-10 is 1.56 μmol/g/h, achieving 5.38-folds higher than that of In₂O₃ (0.29 μmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In₂O₃ on Ag-In₂O₃ compounds. In Ag-In₂O₃ compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In₂O₃, resulting in the photocatalytic activity enhancement of Ag-In₂O₃ compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Core-shell structured Z-scheme Ag2S/AgIO3 composites for photocatalytic organic pollutants degradation

Constructing direct Z-scheme system is a promising strategy to boost the photocatalytic performance for pollution waters restoration, but it is of great challenge because of the requirement of appropriately staggered energy band alignment and intimate interfacial interaction between semiconductors. Herein, a class of core-shell structured Ag₂S-AgIO₃ Z-scheme heterostructure photocatalysts are designed and developed. Ag₂S is generated by the in-situ ion exchange reaction and anchored on the surface of AgIO₃, so the intimate interface between AgIO₃ and Ag₂S is realized. Integration of AgIO₃ and Ag₂S extends the ultraviolet absorption of AgIO₃ to Vis-NIR region, and also promote the charge separation and migration efficiency, contributing to the enhanced photocatalysis activity for composite catalysts. The optimal Ag₂S-AgIO₄-4 catalyst exhibits a MO photo-degradation rate constant of 0.298 h^-1, which reaches 5.77 and 11.4-folds higher than that of AgIO₃ (0.044 h^-1) and Ag₂S (0.024 h^-1). The as-obtained composite catalyst exhibits universally photocatalytic activity in disintegrating diverse industrial pollutants and pharmaceuticals. Particularly, driven by natural sunlight, the Ag₂S-AgIO₄-4 can effectively decompose MO. A plausible Z-scheme photocatalytic mechanism and reaction pathways of MO degradation over composite catalyst are systemically investigated and proposed.

One-step synthesis of visible light CO2 reduction photocatalyst from carbon nanotubes encapsulating iodine molecules

We describe the synthesis and visible-light CO2 photoreduction catalytic properties of a three-component composite consisting of AgI, AgIO3, and single-walled carbon nanotubes (SWCNTs). The catalyst is synthesized by immersing SWCNTs encapsulating iodine molecules in AgNO3 aqueous solution, during which neutral iodine (I2) molecules encapsulated in SWCNTs transform disproportionately to I5+ (AgIO3) and I- (AgI), as revealed from the characterization of the composite by Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In addition, photoirradiation experiments using a solar-simulator (AM1.5G) showed that the obtained three-component composite works as a CO2 photoreduction catalyst under visible light despite the wide band gap of AgIO3, suggesting possible transfer of the visible light-excited electron from AgI via SWCNTs.

Plasmonic Photocatalysts for Sunlight-Driven Reduction of CO2 : Details, Developments, and Perspectives

Plasmonic photocatalysis is among the most efficient processes for the photoreduction of CO₂ into valuable fuels. The formation of localized surface plasmon resonance (LSPR), energy transfer, and surface reaction are the significant steps in this process. LSPR plays an essential role in the performance of plasmonic photocatalysts as it promotes an excellent, light absorption over a broad wavelength range while simultaneously facilitating an efficient energy transfer to semiconductors. The LSPR transfers energy to a semiconductor through various mechanisms, which have both advantages and disadvantages. This work points out four critical features for plasmonic photocatalyst design, that is, plasmonic materials, size, shape of plasmonic nanoparticles (PNPs), and the contact between PNPs and semiconductor. Various developed plasmonic photocatalysts, as well as their photocatalytic performance in CO₂ photoreduction, are reviewed and discussed. Finally, perspectives of advanced architectures and structural engineering for plasmonic photocatalyst design are put forward with high expectations to achieve an efficient CO₂ photoreduction shortly.

An in situ Bi-decorated BiOBr photocatalyst for synchronously treating multiple antibiotics in water

Currently, there is an urgent demand for developing new materials to remove antibiotics in the water environment, especially for the simultaneous degradation of multiple antibiotics. Here, we fabricated a novel Bi/BiOBr heterostructure via an in situ solvothermal strategy, and it exhibited excellent visible-light-responsive photocatalytic activity for synchronously removing multiple antibiotics coexisting in water. The Bi nanoparticles could extend the light absorption spectra of the sample and further facilitate electron-hole pair separation. The in-depth electron spin resonance (ESR) results confirm that the active species in Bi/BiOBr are holes (h⁺) and superoxide radicals (·O₂ ^-) under irradiation, and it is also proved that Bi could selectively reduce the formation of ·O₂ ^- in the BiOBr matrix. The coexisting system of TC (tetracycline hydrochloride), CIP (ciprofloxacin) and DOX (doxycycline) could be simultaneously photodegraded to approximately 0% within 30 min by the Bi/BiOBr photocatalyst.

Fluorescent sensing of ascorbic acid based on iodine induced oxidative etching and aggregation of lysozyme-templated silver nanoclusters

In this work, we developed a sensitive and highly selective fluorescent approach for the detection of ascorbic acid (AA) by taking advantage of the oxidative etching effect of iodine (I₂) on the lysozyme-stabilized silver nanoclusters (dLys-AgNCs) with fluorescence quenching. I₂ could be produced from the redox reaction between iodate (IO₃^-) and AA, and thus the fluorescence intensity of dLys-AgNCs was turned off significantly in the coexistence of IO₃^- and AA. The fluorescence quenching of dLys-AgNCs had a good linear relationship with AA concentration, which allowed the detection of AA in the range from 0.05 to 45.0 μmol L^-1 with a detection limit of 20 nmol L^-1. The quenching mechanism was elucidated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) measurements, confirming that the fluorescence quenching of the dLys-AgNCs was attributed to the oxidative etching of the in situ generated I₂, inducing aggregation of the dLys-AgNCs probe by forming Ag@AgI nanocomposite. The dLys-AgNCs probe exhibited excellent selectivity for AA sensing over several common reducing agents tested. Moreover, this approach was extended to the detection of AA in orange juice and urine with recovery rates in the range of 96.0% (RSD: 4.11) to 100.9% (RSD: 3.28) and 94.5% (RSD: 6.40) to 99.2% (RSD: 5.36), respectively.

In situ solid-state fabrication of hybrid AgCl/AgI/AgIO3 with improved UV-to-visible photocatalytic performance

The AgCl/AgI/AgIO₃ composites were synthesized through a one-pot room-temperature in situ solid-state approach with the feature of convenient and eco-friendly. The as-prepared composites exhibit superior photocatalytic performance than pure AgIO₃ for the degradation of methyl orange (MO) under both UV and visible light irradiation. The photodegradation rate toward MO of the AgCl/AgI/AgIO₃ photocatalyst can reach 100% after 12 min irradiation under UV light, or 85.4% after 50 min irradiation under visible light, being significantly higher than AgCl, AgI, AgIO₃ and AgI/AgIO₃. In addition, the AgCl/AgI/AgIO₃ photocatalyst possesses strong photooxidation ability for the degradation of rhodamine B (RhB), methylene blue (MB), phenol, bisphenol A (BPA) and tetracycline hydrochloride under visible light irradiation. The reactive species capture experiments confirmed that the h⁺ and •O²⁻ play an essential role during the photocatalytic process under UV light or visible light irradiation. The enhanced effect may be beneficial from the enhanced light adsorption in full spectrum and increased separation efficiency of photogenerated hole-electron pairs, which can be ascribed to the synergistic effect among AgCl, AgI and AgIO₃ nanoplates in AgCl/AgI/AgIO₃ composites.

Advances in Photocatalytic CO₂ Reduction with Water: A Review

In recent years, the increasing level of CO₂ in the atmosphere has not only contributed to global warming but has also triggered considerable interest in photocatalytic reduction of CO₂. The reduction of CO₂ with H₂O using sunlight is an innovative way to solve the current growing environmental challenges. This paper reviews the basic principles of photocatalysis and photocatalytic CO₂ reduction, discusses the measures of the photocatalytic efficiency and summarizes current advances in the exploration of this technology using different types of semiconductor photocatalysts, such as TiO₂ and modified TiO₂, layered-perovskite Ag/ALa₄Ti₄O₁₅ (A = Ca, Ba, Sr), ferroelectric LiNbO₃, and plasmonic photocatalysts. Visible light harvesting, novel plasmonic photocatalysts offer potential solutions for some of the main drawbacks in this reduction process. Effective plasmonic photocatalysts that have shown reduction activities towards CO₂ with H₂O are highlighted here. Although this technology is still at an embryonic stage, further studies with standard theoretical and comprehensive format are suggested to develop photocatalysts with high production rates and selectivity. Based on the collected results, the immense prospects and opportunities that exist in this technique are also reviewed here.

Surface plasmon polariton-induced hot carrier generation for photocatalysis

Non-radiative plasmon decay in noble metals generates highly energetic carriers under visible light irradiation, which opens new prospects in the fields of photocatalysis, photovoltaics, and photodetection. While localized surface plasmon-induced hot carrier generation occurs in diverse metal nanostructures, inhomogeneities typical of many metal-semiconductor plasmonic nanostructures hinder predictable control of photocarrier generation and therefore reproducible carrier-mediated photochemistry. Here, we generate traveling surface plasmon polaritons (SPPs) at the interface between a noble metal/titanium dioxide (TiO₂) heterostructure film and aqueous solution, enabling simultaneous optical and electrochemical interrogation of plasmon-mediated chemistry in a system whose resonance may be continuously tuned via the incident optical excitation angle. To the best of our knowledge, this is the first experimental demonstration of SPP-induced hot carrier generation for photocatalysis. We found electrochemical photovoltage and photocurrent responses as SPP-induced hot carriers drive both solution-based oxidation of methanol and the anodic half-reaction of photoelectrochemical water-splitting in sodium hydroxide solution. A strong excitation angle dependence and linear power dependence in the electrochemical photocurrent confirm that the photoelectrochemical reactions are SPP-driven. SPP-generated hot carrier chemistry was recorded on gold and silver and with two different excitation wavelengths, demonstrating potential for mapping resonant charge transfer processes with this technique. These results will provide the design criteria for a metal-semiconductor hybrid system with enhanced hot carrier generation and transport, which is important for the understanding and application of plasmon-induced photocatalysis.

Iodide surface decoration: a facile and efficacious approach to modulating the band energy level of semiconductors for high-performance visible-light photocatalysis

Iodide surface decoration enables the wide-band-gap Bi₂O₂CO₃ to possess a continuously tunable band gap and profoundly boosted visible-light photocatalytic performance for dye degradation and NO removal.

Synthesis of BiOI nanosheet/coarsened TiO2 nanobelt heterostructures for enhancing visible light photocatalytic activity

BiOI nanosheet/coarsened TiO₂ nanobelt heterostructure composites (BiOI/TiO₂ CNHs) were prepared via an efficient hydrothermal method.