Photocatalysis is considered as one of the most appealing advanced technology in solution to the environmental problems and non-renewable energy resources depletion with a variety of applications such as synthesis, industry, water, and environmental remediation. [1][2][3][4][5] Although enormous research has been carried out with impressive advancement in photoactive materials, the process of photocatalysis still suffers from low efficiency and poor stability that is far below the requisites for practical applications. The three main key steps that governs photocatalysis includes light absorption, generation of electron-hole pairs, followed by their migration from the bulk to the surface and initiation of interfacial redox reactions upon their arrival at the active sites. [6,7] In order to boost up the photocatalytic efficiency, various approaches have been adopted such as doping, crystal facet exposure, synthesis parameters, reaction environments, hybridization, dimensions, and morphology tuning of photocatalysts. [8][9][10][11] However, the efficiency of these photocatalysts is still limited by their cost, wide band gap, lower stability and poor charge transfer kinetics. [12] In order to address the aforementioned issues, extensive research has been conducted to increase the surface area, such as nanowires, nanosheets, nanotubes, and other hierarchical nanostructures are developed with abundant active sites for redox reactions. [13][14][15][16][17] Similarly, to enhance charge separation, hetrojunctions were explored utilizing different semiconductors with appreciable band alignment. [18][19][20] Alternatively, effective light absorption with undoubtedly decreased recombination and improved photocatalytic performance through defect engineering have been reported. [21,22] Defects in semiconductors greatly alter carrier concentration and interface reaction affecting the overall process efficiency of a photocatalyst. Thus, defects are the most frequently investigated scenario for tuning the properties of photocatalyst. [23,24] However, defects are detrimental to photocatalysis in regard of the recombination centers and lack detailed explanation in terms of carrier concentration, transfer dynamics, band structure, and interface profiles. [25] The emerging trend of defect engineering still brought the opportunity of deliberately manipulating the photocatalyst properties. Although the influence of defects on photocatalytic performance has been previously elaborated in some reviews, their optimization and intrinsic role in photocatalysis is still elusive. [12,[25][26][27][28] Therefore, some novel strategies based on advanced modeling theoretical and experimental knowledge are of great need to elucidate the role of defects in photocatalysis. Subsequently, it has been suggested that different synthesis strategies offer different mechanisms thus altering the band structure, carrier mobility, and so reactivity (Figure 1). It therefore remains a challenging task to account the relationship between defect chemistry and per...

A novel method based on conversion of chlorinated volatile organic compounds (CVOCs) to chlorine using a new type of column packed with nanometer TiO2 coupled with chemiluminescence (CL) has been developed for determination of them in workplace air. CVOCs are converted to chlorine by nanometer TiO2 at 220 degrees C. The Cl2 that is produced is selectively enriched on the column and subsequently released from the column at 600 degrees C. The Cl2 that is released is determined using a postcolumn CL detector. The CL intensity was linear with CCl4 in the range of 0.1-380 ppm, and the detection limit was 40 ppb (S/N = 3). Higher sensitivity could be acquired by using a larger volume of enrichment A similar procedure could be used for the determination of other CVOCs. CL intensities of CH2Cl2, CHCl3, and CCl4 at the same concentration increased in the order CH2Cl2 < CHCl3 < CCl4. The method has been successfully applied to the determination of CCl4 in workplace air, where 0.15-150 ppm CCl4 would be detected. The possible mechanism for the long lifetime of the column packed with nanometer TiO2 was tested using Raman spectrometer, X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the column packed with nanometer TiO2 could be operated in the reversible mode for determination of CVOCs under the present conditions. The method would be potentially applied to the analysis of other chlorinated compounds in environment, such as persistent organic pollutants.

To achieve high sensitivity and uniformity simultaneously in a surface-enhanced Raman scattering (SERS) substrate, this paper presents the preparation of a flexible and transparent three-dimensional (3D) ordered hemispherical array polydimethylsiloxane (PDMS) film. This is achieved by self-assembling a single-layer polystyrene (PS) microsphere array on a silicon substrate. The liquid-liquid interface method is then used to transfer Ag nanoparticles onto the PDMS film, which includes open nanocavity arrays created by etching the PS microsphere array. An open nanocavity assistant soft SERS sample, “Ag@PDMS,” is then prepared. For electromagnetic simulation of our sample, we utilized Comsol software. It has been experimentally confirmed that the Ag@PDMS substrate with silver particles of 50 nm in size is capable of achieving the largest localized electromagnetic hot spots in space. The optimal sample, Ag@PDMS, exhibits ultra-high sensitivity towards Rhodamine 6 G (R6G) probe molecules, with a limit of detection (LOD) of 10−15 mol/L, and an enhancement factor (EF) of ∼1012. Additionally, the substrate exhibits a highly uniform signal intensity for probe molecules, with a relative standard deviation (RSD) of approximately 6.86%. Moreover, it is capable of detecting multiple molecules and can perform real detection on non-flat surfaces.

No abstract

We report a low-cost fabrication strategy to prepare a large-area carbon fiber cloth (CFC) coated by Ag nanoparticles (AgNPs) as a flexible surface-enhanced Raman scattering substrate. AgNPs were deposited on a hydrophilized CFC by ultraviolet (UV) irradiation of AgNO3 solution, named UV-AgNPs@CFC. The UV irradiation duration and AgNO3 solution concentration can affect the AgNPs structure. SERS property is investigated using rhodamine 6 G (R6G) and crystal violet (CV) as standard analytes and the detection concentration level is down to 10−10 mol/L. The analytical enhancement factor can reach 1.22 × 109. Also, the substrate has remarkable stability and uniformity; the relative standard deviation (RSD) of the characteristic peak calculated at 611cm−1 is 14.4%. Additionally, the UV-AgNPs@CFC substrate can detect two different molecules simultaneously. Our flexible SERS substrate enables efficient molecular extraction and Raman measurements on the curved surface of apples. The detection concentration level for CV is down to 10−5 mol/L. Moreover, the electric field distribution of the hybrid structure is simulated by the finite difference time domain and COMSOL Multiphysics software, and the maximal electric field intensity is 25.7 V/m. Meanwhile, we deposited AgNPs on the TiO2 nanorods-modified CFC (TiO2-CFC) by UV irradiation. A reusable self-cleaning UV-AgNPs@TiO2-CFC substrate was fabricated.