Synthesis of crystal-phase and color tunable mixed anion co-doped titanium oxides and their controllable photocatalytic activity

B and N mixed anions co-doped titania with various crystal phases such as anatase,brookite,and rutile were successfully synthesized by a hydrothermal synthesis followed by heat treatment in an ammonia gas atmosphere at 550-650℃(denoted as BN-Ana_x,BN-Bro_x,and BN-Rut_x,x is the treatment temperature).The colors of as-prepared BN-Ana,BN-Bro,and BN-Rut are red,yellow-green,and cyangreen,respectively.The color changing mechanism of titania was related to their various band gap structure and the existence of B-N bonding.The nitridation temperature exhibits effective color changing compared to that of nitridation time.The different phases of the mixed anion codoped titania possess different photocatalytic deNO_(x) activity.The BN-Ana and BN-Rut show poor photocatalytic deNO_(x) activity,while the BN-Bro shows excellent photocatalytic deNO_(x) activity,better than that of standard titania photocatalyst Degussa P25.The colorful titania with low-photocatalytic activity is heavy metal elements free,indicating their possible applications as nontoxic color pigments or novel cosmetic raw materials.

Morphology control of aluminum nitride(AlN)for a novel high-temperature hydrogen sensor

Hydrogen is a promising renewable energy source for fossil-free transportation and electrical energy generation.However,leaking hydrogen in high-temperature production processes can cause an explosion,which endangers production workers and surrounding areas.To detect leaks early,we used a sensor material based on a wide bandgap aluminum nitride(AlN)that can withstand a high-temperature environment.Three unique AlN morphologies(rod-like,nest-like,and hexagonal plate-like)were synthesized by a direct nitridation method at 1400℃usingγ-AlOOH as a precursor.The gas-sensing performance shows that a hexagonal plate-like morphology exhibited p-type sensing behavior and showed good repeatability as well as the highest response(S=58.7)toward a 750 ppm leak of H2 gas at high temperature(500°C)compared with the rod-like and nest-like morphologies.Furthermore,the hexagonal plate-like morphology showed fast response and recovery times of 40 and 82 s,respectively.The surface facet of the hexagonal morphology of AlN might be energetically favorable for gas adsorption–desorption for enhanced hydrogen detection.

Recent research progress on mixed valence state tungsten based materials

Synthesis and characterization of tungsten based mixed valence state nanoparticles and their novel applications are reviewed.The mixed valence state tungsten based homogeneous nanomaterials such as bronze structure M_(x)WO_(3)(M=Na^(+),K^(+),Rb^(+),Cs^(+),NH_(4)^(+),etc.)and tungsten sub-oxide W_(18)O_(49) possess excellent infrared(IR)light shielding property,implying their great potential applications on heat ray shielding and indoor energy saving effect in summer season.Also,some novel properties such as electric conductivity,bio thermal therapy function and electrochromic properties of mixed valence state tungsten based materials are introduced.The design of components,formation of composites and structure control of thin films are expected to realize the property enhancement and candidates for practice application as window materials.The multifunc-tionality of the mixed valence state based composites also implies great potential on novel applications of various building materials.

SnO-SnO_(2) modified two-dimensional MXene Ti3C2Tx for acetone gas sensor working at room temperature

Acetone,as widely used reagents in industry and laboratories,are extremely harmful to the human.So the detection of acetone gas concentrations and leaks in special environments at room temperature is essential.Herein,the nanocomposite combining SnO-SnO_(2)(p-n junction)and Ti_(3)C_(2)T_(x) MXene was successfully synthesized by a one-step hydrothermal method.Because of the existence of a small amount of oxygen during the hydrothermal conditions,part of the p-type SnO was oxidized to n-type SnO_(2),forming in-situ p-n junctions on the surface of Sn O.The hamburger-like SnO-SnO_(2)/Ti_(3)C_(2)T_(x) sensor exhibited improved acetone gas sensing response of 12.1(R_(g)/R_(a))at room temperature,which were nearly 11 and 4 times higher than those of pristine Ti_(3)C_(2)T_(x) and pristine SnO-SnO_(2),respectively.Moreover,it expressed a short recovery time(9 s)and outstanding reproducibility.Because of the different work functions,the Schottky barrier was formed between the SnO and the Ti_(3)C_(2)T_(x) nanosheets,acting as a hole accumulation layer(HALs)between Ti_(3)C_(2)T_(x) and tin oxides.Herein,the sensing mechanism based on the formation of hetero-junctions and high conductivity of the metallic phase of Ti_(3)C_(2)T_(x) MXene in SnO-SnO_(2)/Ti_(3)C_(2)T_(x) sensors was discussed in detail.

A facile method for preparation of uniformly decorated-spherical SnO2 by CuO nanoparticles for highly responsive toluene detection at high temperature

We reported a facile preparation of a uniform decoration of spherical n-type SnO2 by p-type CuO nanopa rticles as well as their utilization for enhanced performance on toluene gas detection.CuO nanoparticles and spherical SnO2 were synthesized by a facile non-hydrolytic solvothermal reaction,which could easily control their morphology.A uniform CuO nanoparticles decoration onto spherical SnO2 was achieved by a simple sonication and vigorous stirring at room tempe rature.We revealed orga nic solvents used in the oxide synthesis had a considerable influence on its surface charge that was beneficial for a uniformly electrostatic self-decoration between positively charged p-type CuO nanoparticles and negatively charged n-type spherical SnO2.Interestingly,CuO was partially reduced to Cu metal during high concentration of toluene exposure destroying p-n contact and developing new metal-semiconductor contact so-called ohmic junction,resulting in extraordinarily responsive and selective to toluene gas at 400℃as compared to a single p-CuO and n-SnO2.It was also found that the amount of particle decoration had an influence on sensor response and resistance.The optimum amount of CuO nanoparticle decoration was0.1 mmol on 0.5 mmol SnO2.The re s ponse(S=Ra/Rg)and selectivity of CuO/S nO2 based material toward the exposure of 75 ppm toluene had reached to such high as 540 and 5,respectively.The effect of p-n heterojunction and metal-semiconductor contact on the gas sensing mechanism of p-type CuO/n-type SnO2 was discussed.Furthermore,by decorating with CuO nanoparticles,CuO/SnO2 morphology was well-maintained after gas sensing evaluation demonstrated its excellency for high temperature toluene gas sensor application.

Improved thermochromic and photocatalytic activities of F-VO_(2)/ Nb-TiO_(2) multifunctional coating films

Multifunctional photocatalytic and thermochromic composites consisting of fluorine-doped vanadium dioxide(F-VO_(2))and niobium-doped TiO_(2)(NTO)were prepared by a simple physical mixing.The composites exhibited a higher thermochromic activity and nitrogen oxide(NO_(x))decomposition activity than that of pristine VO_(2)/NTO.Both VO_(2) and NTO materials were synthesized using an environmentally friendly soft chemical solvothermal/hydrothermal process,which produced NTO nanoparticles with a controllable morphology and particle size by changing the ratio of ethanol and acetic acid sol-vent.F-VO_(2)/NTO showed a better multifunctionality of thermochromic and photocatalytic activities than those of VO_(2)/NTO samples.The coexistence coating films showed a better effect on thermochromic and deNO_(x)(NO_(x) reduction)activity than those of double-sided films for F-VO_(2)/NTO samples.The best thermochromic and photocatalytic activities obtained from sample F-VO_(2)/NTO 60 showed the ΔT_(1500 nm)[difference of transmittance(ΔT)at the wavelength of 1500 nm under 25°C and 95°C]of up to 29.5%and deNO_(x) activity of up to 40%at λ>290 nm under mercury lamp irradiation.The use of F-VO_(2)/NTO coexistence coating films showed the appropriateness for multifunctional materials.

A simple and novel effective strategy using mechanical treatment to improve the oxygen uptake/release rate of YBaCo_(4)O_(7+δ) for thermochemical cycles

In recent years,oxygen storage materials(OSMs)have been widely used in many fields.It would be particularly important for researchers to design high-oxygen-uptake/release-rate materials.In this study,various synthesis processes were used to successfully synthesize YBaCo_(4)O_(7+δ)and comprehensively investigate their potential applications.Compa red with traditional solid-state reaction method and co-precipitation method,the results demonstrated that the utilization of mechanical ball milling treatment on co-precipitated precursors could lead to samples with reversible oxygen uptake/release under an oxidative atmosphere at low temperatures.The resultant materials exhibited fast oxygen absorption/desorption rate that could uptake/release oxygen directly to the equilibrium state within 9 min and20 min,respectively.The mechanochemically ball-milled sample possessed outstanding oxygen sto rage performance,which could be attributed to their small particle size,the active outer surface of particles,large specific surface area,and relatively low activation energy.Moreover,the ball-milled sample also exhibited excellent cycling stability during relatively short time spacing.TG results also demonstrated that the ball-milled samples could reversibly uptake/release 2.90 wt.%of excess oxygen(while only 0.70 wt.%for solid-state samples)by adjusting the ambient temperature under pure O_(2) atmosphere,which would make them promising candidates in various applications.This research demonstrated that mechanical treatment could be an effective strategy to tune the properties and oxygen storage capacity(OSC)performances of YBaCo_(4)O_(7+δ).