Tu Hu

Synthesis of Ag2CO3/Bi2WO6 heterojunctions with enhanced photocatalytic activity and cycling stability

Hierarchical Bi2WO6 nanoarchitectures with a size of 2–3 μm were prepared via a facile microwave-assisted solution-phase reaction process. Monodisperse spherical Ag2CO3 nanoparticles with an average size of about 10 nm were deposited onto the surface of the Bi2WO6 nanoarchitectures to form a novel Ag2CO3/Bi2WO6 heterojunction structure through a facile in situ precipitation–deposition method. The obtained samples were characterized using XRD, XPS, SEM, TEM (HRTEM), UV-vis DRS and nitrogen adsorption–desorption techniques. The photocatalytic evaluation demonstrates that the decoration with Ag2CO3 nanoparticles significantly enhances the photocatalytic activity of Bi2WO6 and the photocatalytic performance is greatly influenced by the content of deposited Ag2CO3. The 30 wt% Ag2CO3-loaded Bi2WO6 sample exhibited the highest photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation. Meanwhile, it also possesses excellent cycling stability and superior photocatalytic performance toward other pollutants. The dramatically enhanced photocatalytic activity and stability can be mainly ascribed to well-matched energy bands and heterojunctions between Ag2CO3 and Bi2WO6, which can effectively improve the separation of photo-induced electron–hole pairs at the heterojunction interfaces.

Controllable synthesis porous Ag2CO3 nanorods for efficient photocatalysis

The novel porous Ag2CO3 nanorods were facilely synthesized via a one-pot aqueous solution reaction at room temperature. The crystalline phase and size distribution of the nanorods were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. In addition, the porous feature of nanorods was confirmed by transmission electron microscopy (TEM) and nitrogen adsorption-desorption. The morphology and size of the Ag2CO3 crystal can be regulated via the choice of dispersing agents and adding approaches of reactants. Photocatalytic results show that the porous Ag2CO3 nanorods exhibit excellent photodegradation of rhodamine B (RhB) under visible-light irradiation, particularly the photoactivity performance and stability can be further improved in the presence of sodium bicarbonate (NaHCO3). It is indicated that NaHCO3 can prevent effectively the photocorrosion and promote the probability of electron-hole separation.

Selective Adsorption of Ag+ on a New Cyanuric-Thiosemicarbazide Chelating Resin with High Capacity from Acid Solutions

A new cyanuric-thiosemicarbazid (TSC-CC) chelating resin was synthesized and employed to selectively adsorb Ag+ from acid solutions. The effects of acid concentration, initial concentration of Ag+, contact time and coexisting ions were investigated. The optimal acid concentration was 0.5 mol/L. The adsorption capacity of Ag+ reached 872.63 mg/g at acid concentration of 0.5 mol/L. The adsorption isotherm was fitted well with the Langmuir isotherm model and the kinetic data preferably followed the pseudo-second order model. The chelating resin showed a good selectivity for the Ag+ adsorption from acid solutions. Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Scanning electron microscopy/energy dispersive spectrometer (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) were used to study the adsorption mechanism. The chelating and ionic interaction was mainly adsorption mechanism. The adsorbent presents a great potential in selective recovery Ag+ from acid solutions due to the advantage of high adsorption capacity and adapting strongly acidic condition. The recyclability indicated that the (TSC-CC) resin had a good stability and can be recycled as a promising agent for removal of Ag+.

High temperature dielectric properties of spent adsorbent with zinc sulfate by cavity perturbation technique

Dielectric properties of spent adsorbent with zinc sulfate are investigated by cavity perturbation technique at 2450MHz from 20°C to approximately 1000°C. Two weight loss stages are observed for spent adsorbent by thermogravimetric-differential scanning calorimeter (TG-DSC) analysis, and zinc sulfate is decomposed to ZnO·2ZnSO4 and ZnO at about 750°C and 860°C. Microwave absorption capability of ZnSO4 increases with increasing temperature and declines after ZnO generation on account of the poor dielectric properties. Dielectric properties of spent adsorbent are dependent on apparent density and noticed an interestingly linearly relationship at room temperature. The three parameters increase gently from 20°C to 400°C, but a sharp increase both in real part and imaginary part are found subsequently due to the volatiles release and regeneration of carbon. And material conductivity is improved, which contributes to the π-electron conduction appearance. Relationship between penetration depth and temperature further elaborate spent adsorbent is an excellent microwave absorber and the microwave absorption capability order of zinc compounds is ZnO·2ZnSO4, ZnSO4 and ZnO. Heating characteristics suggest that heating rate is related with dielectric properties of materials. The pore structures of spent adsorbent are improved significantly and the surface is smoother after microwave-regeneration.

Synergetic surface modification effect of argon and oxygen for diamond films by MPCVD

Abstract Diamond films were synthesized in a CH4-H2 system with good surface quality by adjusting the additive amount of argon and oxygen gas. The diamond phase content and surface roughness of samples are 86.1% and 81.5 nm, respectively. The results indicate that only Ar addition will decrease the purity of diamond films, whereas Ar-O2 mixed gas can further increase the diamond phase content. It is worth noting that the content of diamond phase has no significant increase when O2 flow exceed 1 sccm. The surface roughness reduced from 199.8 to 81.5 nm by the addition of 14 sccm Ar and 1 sccm O2, and the surface quality will be deteriorated in case of further increasing O2 or decreasing Ar concentration. Meanwhile, the growth rate under different conditions and the synergetic surface modification effect of Ar-O2 mixed gas for diamond films growth process were discussed.

Microwave roasting of agglomerated flux for submerged-arc welding

Abstract A microwave (MW) roasting experiment of agglomerated flux for submerged-arc welding was carried out. The MW heating characteristics of agglomerated flux and influence of roasting temperature on weld surface were investigated. It was found that the heating rate of agglomerated flux becomes faster with the increase of MW powder. It only takes 17 min to heat the sample of 600 g from room temperature to 720°C. A neat and smooth weld surface can be obtained for agglomerated flux roasted by MW heating at 680°C for 30 min. Compared with conventional roasting methods, MW roasting has the advantage of lower temperature and shorter time.

Fabrication of Cu Based Metallic Binder for Diamond Tools by Microwave Pressureless Sintering

Microwave pressureless sintering (MPS) method is successfully applied in the fabrication of Cu based metallic matrix for diamond tools. The main purpose of this work is to obtain better mechanical properties when the metal binder of the diamond tools was prepared by the MPS method. The orthogonal experimental method is adopted to design the sintering process parameters. The optimized experimental conditions are suggested as 880 °C of sintering temperature, 375 MPa of cold pressure, and 35 min of withholding time. The contrastive investigation of the MPS and conventional pressureless sintering (CPS) are performed under optimized conditions. The microstructures information are obtained by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and the necessary mechanical properties, such as relative density, hardness, and flexural strength are tested. Experimental results show that the MPS method, compared with CPS, can significantly improve the mechanical properties of the metallic matrix. The factors of relative density, hardness, and flexural strength increase 1.25%, 3.86%, and 6.28%, respectively. The possible sintering mechanism of the MPS method is also discussed. This work may provide a reference for the fabrication of metal-based diamond tools by microwave heating method.

Enhanced and selective adsorption of Hg2+ to a trace level using trithiocyanuric acid-functionalized corn bract

A novel trithiocyanuric acid-modified corn bract (TCA-CCB) was prepared, and its removal properties for Hg2+ were investigated. TCA-CCB showed a remarkable absorbability for Hg2+ in mixed ion solutions. Adsorption kinetics experiments indicated that the removal of Hg2+ on TCA-CCB was quick, with a removal rate of 99.07% within 5 min. In addition, the removal rate of Hg2+ exceeded 98% over all pH conditions. The adsorption process can be best described by pseudo-second-order kinetic and Hill isotherm models. The saturated adsorption capacity of TCA-CCB for Hg2+ was 390 mg/g. The TCA-CCB could efficiently adsorb Hg2+ from the simulated wastewater and reduce the Hg2+ concentration from 10 ppm to 12.35 ppb, which was lower than the greatest allowable value of 50 ppb and satisfied the emission standards required by the Chinese government. Moreover, the removal rate of Hg2+ was beyond 99% after three cycles. The results of the zeta potential and X-ray photoelectron spectroscopy (XPS) implied that the chelation and ion exchange between amino/thiol groups and Hg2+ played a significant role in the improvement of the adsorption properties. The corn bract modified by trithiocyanuric acid exhibits apparent advantages in the removal of Hg2+ from ppm to ppb due to its high selectivity, adsorption capacity and stability.

Microwave heating behaviors of used mercury-containing catalysts

Abstract Heating characteristics of two types of used mercury-containing catalysts with different mercury content in microwave field were studied. Spent mercury catalysts were proved to be good microwave receptors. Heating curves were analyzed using heat transfer equation. With microwave heating, the sample temperature increased linearly, then increased gradually with considering heat loss, and finally reached an equilibrium value. Effects of material mass, microwave input power and particle size on heating behaviors were investigated. A proper material mass fitted with microwave power can lead to higher average heating rate and equilibrium temperature. Sample temperature increased with increasing input power at a constant material mass. Average heating rate was linearly related to input power. A good linear fitting relation between equilibrium temperature and input power was observed especially for catalyst support activated carbon and used low-level mercury catalysts.

Utilization of Pine Nut Shell for Preparation of High Surface Area Activated Carbon by Microwave Heating and KOH Activation

Pine nut shell is as raw material for preparation of high surface area activated carbon (HSAAC) by microwave induced KOH activation. The effects of microwave power, activation duration and KOH/C mass rate (R) on the iodine adsorption capability and activated carbon yield were investigated. Additionally the surface characteristics of HSAAC were characterized by nitrogen adsorption isotherms and SEM The operating variables were optimized utilizing the response surface methodology and were identified microwave power 738W, activation duration 17 min, and R 4, corresponding to a yield of 46.28 % and an iodine number of 2154 mg/g. The key pore structure parameters of HSAAC such as the Brunauer-Emmett-Teller (BET) surface area and total pore volume were estimated to be 3819 m2/g and 2.09 mL/g, respectively. The findings strongly support the feasibility of microwave heating for preparation of HSAAC from spent pine nut shell by microwave induced KOH activation.