Detection of intermediates in the TiO_2-assisted photodegradation of Rhodamine B under visible light irradiation

The photocatalytic degradation of dye Rhodamine B （RhB） in the presence of TiO2 nanostdpe or P25 under visible light irradiation was investigated. The degradation intermediates were identified using Infrared spectra （IR spectra）, ^1H nuclear magnetic resonance （^1HNMR） spectra, and gas chromatography-mass spectroscopy （GC-MS）. The IR and the ^1HNMR results showed that the large conjugated chromophore structure of RhB was efficiently destroyed under visible light irradiation in both the photocatalytic systems （TiO2 nanostfipe or P25 and Rhodamine B systems）. GC-MS results showed that the main identified intermediates were ethanediotic acid, 1,2-benzenedicarboxylic acid, 4-hydroxy benzoic acid and benzoic acid, which were almost the same in the TiO2 nanostdpes and P25 systems. This work provides a good insight into the reaction pathway（s） for the TiO2-assisted photocatalytic degradation of dye pollutants under visible light irradiation.

Fast electron transfer and enhanced visible light photocatalytic activity by using poly-o-phenylenediamine modified AgCl/g-C_3N_4 nanosheets

Exfoliation of bulk graphitic carbon nitride(g‐C3N4)into two‐dimensional(2D)nanosheets is one of the effective strategies to improve its photocatalytic properties so that the 2D g‐C3N4 nanosheets(CN)have larger specific surface areas and more reaction sites.In addition,poly‐o‐phenylenediamine(PoPD)can improve the electrical conductivity and photocatalytic activity of semiconductor materials.Here,the novel efficient composite PoPD/AgCl/g‐C3N4 nanosheets was first synthesized by a precipitation reaction and the photoinitiated polymerization approach.The obtained photocatalysts have larger specific surface areas and could achieve better visible‐light response.However,silver chloride(AgCl)is susceptible to agglomeration and photocorrosion.The PoPD/AgCl/CN composite exhibits an extremely high photocurrent density,which is three times that of CN.Obviously enhanced photocatalytic activities of PoPD/AgCl/g‐C3N4 are revealed through the photodegradation of tetracycline.The stability of PoPD/AgCl/CN is demonstrated based on four cycles of experiments that reveal that the degradation rate only decreases slightly.Furthermore,.O2^-and h+are the main active species,which are confirmed through a trapping experiment and ESR spin‐trap technique.Therefore,the prepared PoPD/AgCl/CN can be considered as a stable photocatalyst,in which PoPD is added as a charge carrier and acts a photosensitive protective layer on the surface of the AgCl particles.This provides a new technology for preparing highly stable composite photocatalysts that can effectively deal with environmental issues.

Visible light-driven oxidant-free dehydrogenation of alcohols in water using porous ultrathin g-C_(3)N_(4)nanosheets

Graphitic carbon nitride(g-C_(3)N_(4)) is a fascinating photocatalyst for solar energy utilization in photo-catalysis.Nevertheless,it often suffers from moderate photo-catalytic activity due to its low specific surface area and fast recombination rate of photogenerated electrons upon photo-excitation.Herein,we overcome the bottlenecks by constructing a porous g-C_(3)N_(4) nanosheet(PCNS)through a simple thermal oxidation etching method.Benefited from its porous layer structure,the obtained PCNS exhibits large specific surface area,efficient separation of photogenerated charge carriers,as well as high exposure of active sites.As a result,it is robust and universal in visible light-driven dehydrogenation of alcohols in water under oxidant-free condition.Almost quantitative yields(>99%)of various valuable carbonyl compounds were obtained over PCNS,while bulk g-C_(3)N_(4) was far less efficient.Moreover,the photo-catalyst was highly stable and could be facilely recovered from the aqueous system for efficient reuse.The easy preparation and excellent performance made PCNS a promising and competitive photocatalyst for the solar applications.

Biomolecule-assisted Solvothermal Synthesis and Enhanced Visible Light Photocatalytic Performance of Bi2S3/BiOCl Composites

Novel Bi2S3/BiOCl photocatalysts were successfully synthesized via a facile biomoleculeassisted solvothermal method and biomolecule L-cysteine was used as the sulfur source.The structures,morphology,and optical properties of the synthesized samples were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy,transmission electron microscopy（TEM）,and UV-vis diffuse reflectance spectroscopy（DRS）.The presence of Bi2S3 in the Bi2S3/BiOCl composites could not only improve the optical properties but also enhance the photocatalytic activities for the degradation of Rhodamine B（Rh B） under visible-light irradiation（λ〉420 nm） as compared with single Bi2S3 and BiOCl.Especially,the sample displayed the best performance of the photodegradation when the feed molar ratio of BiCl3 and L-cysteine was 2.4：1,which was about 10 times greater than that of pure Bi OCl.The enhanced photocatalytic activities could be ascribed to the effective separation of photoinduced electrons and holes and the photosensitization of dye.Moreover,the possible photodegradation mechanism was also proposed,and the results revealed that the active holes（h＋） and superoxide radicals（·O2-） were the main reactive species during photocatalytic degradation.

Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO_2 single crystals

Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals（SCs）.To tune their magnetism,Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively.The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2.Meanwhile,a new CuO-like species present in the sample was found to be dissolved after the post-irradiation.Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions,while these ions are directly involved in boosting the absorption in the visible region.

Carbon-nanodot-coverage-dependent photocatalytic performance of carbon nanodot/TiO2 nanocomposites under visible light

Carbon nanodots（CDs） with visible absorption band and TiO2 are integrated to enhance the photosensitivity of TiO2.The CD/TiO2 nanocomposites show obvious CD-coverage-dependent photocatalytic performance. The CD/TiO2 nanocomposites with moderate CD coverge exhibit the highest photocatalytic activity after being irradiated with visible light, which is more excellent than that of TiO2. Too little CD coverage could result in poor visible light absorption, which limits the photocatalytic performance of CD/TiO2 nanocomposites. While, too much CD coverage weakens the photocatalytic activity of CD/TiO2 nanocomposites by restraining the extraction of conduction band electrons within TiO2 to generate active oxygen radicals and the electron transfer（ET） process from CDs to TiO2. These results indicate that rational regulation of CD coverage and the realization of efficient ET process are important means to optimize the photocatalytic performance of CD/TiO2 nanocomposites.

2,5-Diformylfuran production by photocatalytic selective oxidation of 5-hydroxymethylfurfural in water using MoS_(2)/CdIn_(2)S_(4) flower-like heterojunctions

The selective oxidation of 5-hydroxymethylfurfural(HMF) into 2,5-diformylfuran(DFF) is an important reaction for renewable biomass building blocks. Compared with thermal catalytic processes, photocatalytic production of DFF from HMF has attracted tremendous attention. Herein, the MoS_(2)/CdIn_(2)S_(4)(MC)flower-like heterojunctions were prepared and considered as photocatalysts for selective oxidation of HMF into DFF under visible-light irradiation in aqueous solution. Results demonstrated MoS_(2) in MC heterojunction could promote the separation of photoexcited electron-hole pairs, while the amount of MoS_(2) dropping was proved influenced on the photocatalytic performance. 80.93% of DFF selectivity was realized when using 12.5% MC as photocatalyst. In addition, the MC catalyst also showed great potential in transformation of other biomass derived benzyl-and furyl-alcohols. The catalytic mechanism suggested that ·O_(2)^(-) was the decisive active radical for HMF oxidation. Therefore, the MC heterojunction could be applied in photocatalytic conversion of biomass to valuable chemicals under ambient condition.

Effect of pH Values on Photocatalytic Properties of Bi_2WO_6 Synthesized by Hydrothermal Method

Highly crystalline orthorhombic Bi2WO6 powders were hydrothermally synthesized from aqueous solutions of Na2WO4 · 2H2O and Bi （NO3）3 · 5H2O over a wide range of pH. The effect of pH on morphologies, sizes and properties of the Bi2WO6 crystals was investigated. The band gaps of the as-prepared Bi2WO6 were determined from the onset of the absorption edge of UV-vis diffuse reflectance spectra. The methyl orange photodegradation was employed as a probe reaction to test the photocatalytic activity of the as-prepared samples under visible light irradiation. The photocatalytic activities of methyl orange degradation under visible light irradiation are strongly dependent on the pH used in the synthesis. The highest efficiency is observed at pH=7.

Nonylphenol photodegradation by novel ternary MIL-100(Fe)/ZnFe_(2)O_(4)/PCN composite under visible light irradiation via double charge transfer process

Nonylphenol(NP)residues,as a typical endocrine disrupting chemical(EDC),frequently exist in sewage,surface water,groundwater and even drinking water,which poses a serious threat to human health due to its bioaccumulation.In order to remove NP,a series of MIL-100(Fe)/Zn Fe_(2)O_(4)/flake-like porous carbon nitride(MIL/ZC)was synthesized through in-situ synthesis at room temperature.High performance of ternary MIL/ZC is used to degrade NP under visible light irradiation.The results show that 30MIL/ZC2(20 wt.%Zn Fe_(2)O_(4))ternary composite had the best photocatalytic activity(99.84%)when the dosage was 30 mg.Further mechanism analysis shows that the excellent photocatalytic activity of 30MIL/ZC2could be ascribed to the double charge transfer process between flake-like porous carbon nitride(PCN)and other catalysts in the ternary heterojunction,and the separation of photogenerated electron-hole pairs was more effective.In addition,the 30MIL/ZC2 also showed high stability after five cycles of the photodegradation reaction.Furthermore,the active substance(·O_(2)^(-))was considered to be the main active substance in the NP degradation process.Based on the research results,the possible photocatalytic reaction mechanism of 30MIL/ZC2ternary composite was proposed and discussed in detail.

Fabrication of BiVO4：Effect of Structure and Morphology on Photocatalytic Activity and Its Methylene Blue Decomposition Mechanism

BiVO4 photocatalysts were synthesized by a surfactant free hydrothermal method without any further treatments,and characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS）,Raman spectroscopy,and Brunauer-Emmett-Teller（BET） surface area techniques.The photocatalytic activity was evaluated for the degradation of the methylene blue（MB） under visible light irradiation.Seen from the structural and morphological characterization,it is stated that the obtained samples present monoclinic phase,and the pH value has significant influence on the morphologies.The enhanced photocatalytic performance was associated with its crystallinity,unique morphology,band gap energy,BET specific surface area,surface charge and adsorption capacity.The recycle experiments results show that the BiVO4 photocatalysts have excellent photo-stability,and we deduced a possible mechanism by examining the effects of the active species involved in the photocatalytic process for MB photocatalytic degradation.

A High Performance Cobalt-Doped ZnO Visible Light Photocatalyst and Its Photogenerated Charge Transfer Properties

Highly photocatalytically active cobalt-doped ZnO （ZnO：Co） nanorods have been prepared by a facile hydrothermal process. X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering and UV-vis diffuse reflectance spectroscopy confirmed that the dopant ions substitute for some of the lattice zinc ions, and furthermore, that Co〉 and Co〉 ions coexist. The as-prepared ZnO：Co samples have an extended light absorption range compared with pure ZnO and showed highly efficient photocatalytic activity, only requiring 60 rain to decompose -93% of alizarin red dye under visible light irradiation （λ 〉 420 nm）, The photophysical mechanism of the visible photocatalytic activity was investigated with the help of surface photovoltage spectroscopy. The results indicated that a strong electronic interaction between the Co and ZnO was present, and that the incorporation of Co promoted the charge separation and enhanced the charge transfer ability and, at the same time, effectively inhibited the recombination of photogenerated charge carriers in ZnO, resulting in high visible light photocatalytic activity.

Visible light response ZnO-C_(3)N_(4) thin film photocatalyst

Nanoflower-like ZnO-C_(3)N_(4) thin film with a porous net structure was successfully synthesized by a simple chemical corrosion method.The prepared ZnOC_(3)N_(4) thin films presented remarkable photocatalytic activities for the degradation of methyl orange under visible light irradiation,and more than 90%methyl orange was removed from water by ZnO-C_(3)N_(4) composite.Meanwhile,the ZnO-C_(3)N_(4) composite presented an enhanced photocatalytic stability.The loading content of C_(3)N_(4) had a great effect on the photocatalytic performance.Moreover,the photocatalytic activities were higher in acidic media than those in alkaline conditions.The adsorption of methyl orange was enhanced,and the recombination of photogenerated electrons and holes was suppressed with a suitable content of C_(3)N_(4).However,too much loading content of C_(3)N_(4) resulted in a poor dispersion of C_(3)N_(4) as the aggregated C_(3)N_(4) can behave as recombination centers.In addition,the prepared ZnO-C_(3)N_(4) thin film can be used for the water splitting in water-methanol system under simulated solar light irradiation.

High efficiency visible-light-driven Fe_2O_3-xS_x/S-doped g-C_3N_4 heterojunction photocatalysts: Direct Z-scheme mechanism

Several nanoporous Fe2 O3-xSx/S-doped g-C3 N4（CNS） Z-scheme hybrid heterojuctions have been successfully synthesized by one-pot in situ growth of the Fe2O3-xSx particles on the surface of CNS. The characterization results show that S-doping in the g-C3 N4 backbone can greatly enhance the charge mobility and visible light harvesting capability. In addition, porous morphology of hybrid composite provides available open pores for guest molecules and also improves light absorbing property due to existence of multiple scattering effects. More importantly, the Fe2 O3-xSx nanoparticles formed intimate heterojunction with CNS and developed the efficient charge transfer by extending interfacial interactions occurred at the interfaces of both components. It has been found that the Fe2 O3-xSx/CNS composites have an enhanced photocatalytic activity under visible light irradiation compared with isolated Fe2 O3 and CNS components toward the photocatalytic degradation of methylene blue（MB）. The optimal loaded Fe2 O3-xSx value obtained is equal to 6.6 wt% that provided 82% MB photodegradation after 150 min with a reaction rate constant of 0.0092 min（-1） which was faster than those of the pure Fe2 O3（0.0016 min（-1））and CNS（0.0044 min（-1）） under the optimized operating variables acquired by the response surface methodology. The specific surface area and the pore volume of Fe2 O3（6.6）/CNS hybrid are 33.5 m2/g and0.195 cm3/g, which are nearly 3.8 and 7.5 times greater compared with those of the CNS, respectively. The TEM image of Fe2 O3（6.6）/CNS nanocomposite exhibits a nanoporous morphology with abundant uniform pore sizes of around 25 nm. Using the Mott-Schottky plot, the conduction and valence bands of the CNS are measured（at pH = 7） equal to-1.07 and 1.48 V versus normal hydrogen electrode（NHE）, respectively.Trapping tests prove that ·OH-and ·O2-radicals are major active species in the photocatalytic reaction.It has been established that formation of the Z-scheme Fe2 O3（6.6）/CNS heterojunction between CNS and Fe2 O3 directly produces ·OH as well as ·O2-radicals which is consistent with the results obtained from trapping experiments.

Facile synthesis and enhanced visible-light photocatalytic activity of Ti3 ＋-doped Ti02 sheets with tunable phase composition

Ti3＋-doped TiO2 nanosheets with tunable phase composition （doped TiO2 （A/R）） were synthesized via a hydrothermal method with high surface area anatase TiO2 nanosheets TiO2 （A） as a substrate, structure directing agent, and inhibitor; the activity was evaluated using a probe reaction-photocatalytic CO2 conversion to methane under visible light irradiation with H2 as an electron donor and hydrogen source. High-resolution transmission electron microscope （HRTEM）, field emission scanning electron microscope, UV-Vis diffuse reflectance spectra, and X-ray diffraction （XRD） etc., were used to characterize the photocatalysts. XRD and HRTEM measurements confirmed the existence of anatase-rutile phase junction, while Ti3-and single-electron-trapped oxygen vacancy in the doped TiO2 （A/R） photocatalyst were revealed byelectron paramagnetic resonance （EPR） measurements. Effects of hydrothermal synthesis temperature and the amount of added anatase TiO2 on the photocatalytic activity were elucidated. Significantly enhanced photo- catalytic activity of doped TiO2 （A/R） was observed; under the optimized synthesis conditions, CH4 generation rate of doped TiO2 （A/R） was 2.3 times that of Ti3＋-doped rutile TiO2.

Metal-Free-Mediated Oxidation Aromatization of 1,4-Dihydropyridines to Pyridines Using Visible Light and Air

A metal-free and environmentally friendly aerobic aromatization photosensitized by organic dye eosin Y bis(tetrabutyl ammonium salt)(TBA-eosinY)has been developed.With the aid of K_(2)CO_(3),the aerobic catalytic system converts 1,4-dihydropyridines to their corresponding pyridine derivatives efficiently under visible light irradiation(λ=450 nm)at room temperature.

Control of selectivity in organic synthesis via heterogeneous photocatalysis under visible light

Organic synthesis driven by heterogeneous catalysis is a central research theme to both fundamental research and industrial production of fine chemicals.However,the employment of stoichiometric strong oxidizing or reducing reagents(e.g.,K_(2)Cr_(2)O_(7) and LiAlH_(4))and harsh reaction conditions(e.g.,high temperature and pressure)always leads to the products of overreaction and other by-product residues(e.g.,salt and acid waste).Thus the poor control of product selectivity and tremendous energy consumption result in the urgent demand to develop novel technologies for heterogeneous catalysis.Given the current global theme of development in CO_(2) reduction and sustainable energy utilization,one promising protocol is heterogeneous photocatalysis.It enables sustainable solar-to-chemical energy conversion under mild conditions(e.g.,room temperature,ambient pressure,and air as the oxidant)and offers unique reaction pathways for improved selectivity control.To accurately tailor the selectivity of desired products,the electronic structure(e.g.,positions of valence-band maximum and conduction-band minimum),geometric structure(e.g.,nanorod,nanosheet,and porous morphology),and surface chemical micro-environment(e.g.,vacancy sites and co-catalysts)of heterogeneous photocatalysts require rational design and construction.In this review,we will briefly analyze some effective photocatalytic systems with the excellent regulation ability of product selectivity in organic transformations(mainly oxidation and reduction types)under visible light irradiation,and put forward opinions on the optimal fabrication of nanostructured photocatalysts to realize selective organic synthesis.

Novel multi-heterostructured Pt-BiOBr/TiO2 nanotube arrays with remarkable visible-light photocatalytic performance and stability

Unique multiple heterojunction of Pt-BiOBr/TiO2 nanotube arrays（Pt-BiOBr/TNTAs） was achived by successively loading both Pt nanoparticles（NPs） and BiOBr nanoflkes（NFs） on surface of ordered and spaced TiO2 nanotubes（NTs） using anodization followed by solvothermal and sequential chemical bath deposition（S-CBD） method. The fabricated Pt-Bi OBr/TNTAs were fully characterized, and the photocatalytic（PC） activity and stability of PtBiOBr/TNTAs toward degradation of methyl orange（MO） under visible-light irradiation（λ＆gt;400 nm） were evaluated. The results reveal that multiple heterostructures of Pt/TiO2, Pt/BiOBr and BiOBr/TiO2 are constructed among TNTAs substrate, Pt NPs and BiOBr NFs, and the hybrid Pt-BiOBr/TNTAs catalyst exhibits remarkable visible-light PC activity, favourable reusability and long-term stability. The combined effect of several factors may contribute to the remarkable PC performance, including strong visible-light absorption by both Pt NPs and BiOBr NFs, lower recombination rate of photo-generated electrons and holes attributed to the multiple heterojunction, microstructures for facile light injection and adsorption as well as efficient mass transport, and larger specific surface area for enhancing light absorption, increasing the effective contact area between the absorbed dye molecules and catalyst and benefiting the molecule transport of reactants or products.

Simultaneous upconversion luminescence and color centers generated by femtosecond laser irradiation of LiF crystals

We report the upconversion luminescence of lithium fluoride single crystals excited by an infrared femtosecond laser at room temperature. The luminescence spectra demonstrate that upconversion luminescence originates from the color center of F3^＋. The dependence of fluorescence intensity on pump power reveals that a two-photon excitation process dominates the conversion of infrared radiation into visible emission. Simultaneous absorption of two infrared photons is suggested to produce the F3^＋ center population, which leads to the characteristic visible emission. The results are on the reveal and evaluation of the simultaneous two-photon absorption on the green upconversion process.

Photoinduced reaction of potassium alkyltrifluoroborates,sulfur dioxide and para-quinone methides via radical 1,6-addition

A photoinduced reaction of potassium alkyltrifluoroborates,sulfur dioxide,and para-quinone methides under visible light irradiation at room temperature is developed,giving rise to diarylmethyl alkylsulfones in moderate to good yields.This reaction works well under photocatalysis with a broad substrate scope by using DABCO·(SO_(2))_(2)as the source of sulfur dioxide.Mechanistic study shows that this transformation is initiated by alkyl radicals generated in situ from potassium alkyltrifluoroborates in the presence of photocatalyst.The subsequent insertion of sulfur dioxide and radical 1,6-addition of para-quinone methides with alkylsulfonyl radical intermediates afford the corresponding diarylmethyl alkylsulfones.

Synthesis and characterization of Gd-doped PbMoO_(4) nanoparticles used for UV-light-driven photocatalysis

Gd-doped PbMoO_(4) nanoparticles were prepared by a refluxing method at 80℃ for 2 h.Effect of molar content of Gd dopant on phase,morphology and optical properties was studied.The as-prepared Gddoped PbMoO_(4) samples can be indexed to pure tetragonal PbMoO_(4) phase.The particles size of PbMoO_(4) is decreased with increasing in the molar content of Gd dopant from 15.20±3.04 nm for pure PbMoO_(4) to 8.72±1.53 nm for 5 mol% Gd-doped PbMoO_(4).The absorption of 5 mol% Gd-doped PbMoO_(4) nanoparticles shows red-shift caused by lattice distortion of PbMoO_(4).The photocatalytic performance of 5 mol% Gddoped PbMoO_(4) nanoparticles shows the highest degradation of rhodamine B(RhB) of 97.92% under UV radiation and 67.65% under visible radiation because Gd^(3+) dopant as an electron acceptor plays the role in enhancing the separation of electron-hole pair.