In-Situ Hydrothermal Synthesis of Bi–Bi2O2CO3 Heterojunction Photocatalyst with Enhanced Visible Light Photocatalytic Activity

Bismuth containing nanomaterials recently received increasing attention with respect to environmental applications because of their low cost, high stability and nontoxicity. In this work, Bi–Bi_2O_2CO_3 heterojunctions were fabricated by in-situ decoration of Bi nanoparticles on Bi_2O_2CO_3 nanosheets via a simple hydrothermal synthesis approach. X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and high-resolution TEM(HRTEM) were used to confirm the morphology of the nanosheet-like heterostructure of the Bi–Bi_2O_2CO_3 composite. Detailed ultrafast electronic spectroscopy reveals that the in-situ decoration of Bi nanoparticles on Bi_2O_2CO_3 nanosheets exhibit a dramatically enhanced electron-hole pair separation rate, which results in an extraordinarily high photocatalytic activity for the degradation of a model organic dye, methylene blue(MB) under visible light illumination. Cycling experiments revealed a good photochemical stability of the Bi–Bi_2O_2CO_3 heterojunction under repeated irradiation. Photocurrent measurements further indicated that the heterojunction incredibly enhanced the charge generation and suppressed the charge recombination of photogenerated electron-hole pairs.

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.

Photocatalytic degradation of methylene blue by nanostructured Fe/FeS powder under visible light

The photocatalytic performance of mechano-thermally synthesized Fe/FeS nanostructures formed from micron-sized starting materials was compared with that of a thermally synthesized nanostructure with nano-sized precursors in this paper. The properties of as-synthesized materials were studied by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometry（VSM）, diffuse reflectance spectroscopy（DRS）, and ultraviolet–visible（UV-Vis） spectroscopy. The effects of irradiation time, methylene blue（MB） concentration, catalyst dosage, and p H value upon the degradation of MB were studied. Magnetic properties of the samples showed that both as-synthesized Fe/FeS photocatalysts are magnetically recoverable, eliminating the need for conventional filtration steps. Degradation of 5 ppm of the MB solution by mechano-thermally synthesized Fe/FeS with a photocatalyst dosage of 1 kg/m^3 at pH 11 can reach 96% after 12 ks irradiation under visible light. The photocatalytic efficiency is higher in alkaline solution. The kinetics of photocatalytic degradation in both samples is controlled by a first-order reaction. However, the rate-constant value in the thermally synthesized Fe/FeS photocatalyst sample is only 1.5 times greater than that of the mechano-thermally synthesized one.

Rapid Microwave-assisted Hydrothermal Synthesis of Bi0.76Sb1.24S3 and Its Application in the Photocatalytic Degradation of Pollutants by Visible Light Irradiation

Bi（0.76）Sb（1.24）S3 nanocrystals were synthesized by a rapid microwave-assisted hydrothermal method using bismuth nitrate, antimony pentoxide and thioacetamide as starting materials and characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and UV-vis diffuse reflectance spectroscopy（DRS）. The effects of the synthetic condition on the product composition were investigated. The photocatalytic activities of Bi（0.76）Sb（1.24）S3 nanocrystals for the degradation of methyl orange and p-hydroxyazobenzene under visible light irradiation were evaluated. Bi（0.76）Sb（1.24）S3 exhibited good and stable visible light photocatalytic activity.

A Facile Route to Cotton-Like BiOCl Nanomaterial with Enhanced Dye-Sensitized Visible Light Photocatalytic Efficiency

A facile route is developed to fabricate BiOCI porous cotton-like nanostructure by using Bi203 and hydrochlo- ric acid as raw materials. The BiOCI nanomaterial is actually hierarchically structured by numerous ultrathin nanosheets. The nanosheets are around 50-500 nm in lateral size and 2-12 nm in thickness. High-resolution trans- mission electron microscopy and selected-area electron diffraction analyses indicate that single-crystalline BiOCl nanosheets have the predominant growth direction along [110], the bottom and top surfaces are {001} facets, and four lateral surfaces are {110} facets. The BiOCl nanosheets are dominantly enclosed by {001} facets. From the diffuse reflectance spectroscopy spectrum, the light absorption edge and band gap energy （Eg） are estimated to be 416 nm and 2.98eV, respectively. The BiOCl photocatalyst possesses superior activity for methyl orange （MO） degradation under visible light irradiation and the photodegradation efficiency is up to 91.5%/180 min. The correlation between morphology and microstructure with enhanced MO-sensitized photodegradation performance under visible light is investigated.

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.

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.

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.

Study on photocatalytic activity of MoS2/ZnO composite in visible light

A series of MoS_2/ZnO compound photocatalysts with different mass ratios were successfully prepared by hydrothermal method. The X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), scanning electron microscope(SEM) and UV-vis absorption were used to characterize the prepared MoS_2/ZnO photocatalysts. It was proved that the combination of Mo S2 and Zn O can increase the content of oxygen vacancies on surface of Zn O, thus improving the light absorption capacity in visible light region and reducing the band gap of Zn O. And the photocatalytic performance of Zn O was improved. Experimental results show that the MoS_2/ZnO(3 wt%) compound has the highest degradation rate for methylene blue(MB) under visible light, which means that it has the best photocatalytic activity among all the prepared samples.

Surfactant-assisted hydrothermal synthesis of MoS_(2) micro-pompon structure with enhanced photocatalytic performance under visible light

MoS_(2) nanomaterial with the micro-pompon structure was synthesized by a surfactant-assisted hydrothermal method.The morphologies and structures of as-prepared MoS_(2) micro-pompon were investigated by adding different types of surfactants such as cetyltrimethyl ammonium bromide(CTAB),sodium dodecylbenzene sulphonate(SDBS),and polyvinyl pyrrolidone(PVP).The results indicated that the morphology of MoS_(2) could be controlled and changed effectively by the cationic sur-factant of CTAB.A reasonable growth mechanism for hollow structured MoS_(2) micro-pompon by hydrothermal processes was proposed.Further,photocatalytic degradation properties of MoS_(2) micro-pompon under visible light were evaluated by degradation of common organic dyes,which include rhodamine B(RhB),congo red,methyl orange,and methylene blue.The results indicated that MoS_(2) micro-pompon owned the highly selective catalytic ability to RhB with degradation efficiency of 95%in 60 min and 68%in 30 min.With the additive of the surfactant,the MoS_(2)-CTAB sample exhibited an enhanced ability of photocatalytic activity where degradation efficiency was improved to 92%in 30 min.The method employed in this work could be expanded to fabricate other sulfides with the controllable morphology and structure to further regulate the photocatalytic performance.

The electron structure and photocatalytic activity of Ti(IV) doped Bi_2O_3

Density functional theory （DFT） plays a significant role in the development of visible light responsive photocatalysts. Based on the first-principles plane-wave ultrasoft pseudopotential （USPP） method, the crystal structures of α,β,γ, and 5-Bi2O3 were optimally calculated for the total density of states （TDOS） and the partial density of states （PDOS） of Bi, O atoms. The calculation for Ti（IV） doped Bi2O3 supercell was carried out. The effects of Ti（IV）-doping on the electron structures and light absorption properties of various Bi2O3 were analyzed. The results showed that Ti 3d orbital appeared in the forbidden band of Bi2O3 and hybridized with O 2p, Bi 6p orbitals. The narrowed band gap （Eg） and red-shift of light absorption edge are responsible for the enhanced photoeatalytic activity of Bi2O3. The Ⅱ-Bi2O3 and Ti-doped β-Bi2O3 were prepared by a hydrotherrnal synthesis method. The improvement of the photoeatalytic activity of Bi2O3 has also been verified by the characteristics of the UV-vis diffuse reflection spectrum and the experimental evaluation of the photocatalytic degradation of crystal violet in aqueous solution.

Fabrication of NiCoP decorated TiO_(2)/polypyrrole nanocomposites for the effective photocatalytic degradation of tetracycline

Due to the massive discharge of antibiotics in water,it is an urgent matter to remove antibiotics from waste water.The photocatalysts with high stability and activity have attracted extensive attention from researchers.By an in-situ polymerization method,polypyrrole(PPy)was modified on the surface of TiO_(2)(named as TiO_(2)/PPy).By one-step reduction method,NiCoP was grafted on the surface of TiO_(2)/PPy(named as TiO_(2)/PPy/NiCoP)to synthesize the photocatalyst of TiO_(2)/PPy/NiCoP for degradation of tetra-cycline(TC)antibiotic.The characterization results revealed that NiCoP was deposited on the surface of TiO_(2)/PPy successfully.The photocatalytic experiment results illustrated that 83.2%of TC could be de-graded at natural pH with 20 mg of TiO_(2)/PPy/NiCoP in 50 mL of TC solution(10 mg/L)under visible light irradiation.The high catalytic activity is attributed to the attachment of NiCoP on the surface of TiO_(2)/PPy which can enlarge the light response range of TiO_(2)effectively.Scavenger studies revealed that the degra-dation of TC was dominated by•O_(2)−and h+.The photodegradation efficiency of TC with TiO_(2)/PPy/NiCoP still reached over 74%after 5 consecutive cycles,indicating the potential applications in practical wastew-ater.

Nano-photonic crystal formation on highly-doped n-type silicon

We present a novel electrochemical technique for the fabrication of nano-photonic crystal structures. Based on a specially designed electrolyte, porous silicon(PSi) layers with different porosities are possible to be produced on highly-doped n-type silicon substrate by varying the applied current density which determines the size and the morphology of pores. By applying an alternative current density modulation during anodization, porous silicon photonic crystals are obtained using HF-containing electrolyte without oxidizing components. The current burst model(CBM) is employed to interpret the mechanism of the formation of the macropore porous silicon.