Rapid Microwave Hydrothermal Method Research Articles

Microwave‐mediated One‐step Synthesis of CeVO4‐rGO Composites with Enhanced Photocatalytic Activity under Visible Light

AbstractCeVO4‐rGO nanocomposites with varying proportions of CeVO4: rGO (10, 20 and 30 wt% CeVO4) were synthesized by a rapid microwave hydrothermal method. The prepared samples were characterized by X‐ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning/transmission electron microscopy (SEM/TEM), X‐ray photoelectron spectroscopy (XPS), UV‐visible spectroscopy to evaluate their structural, morphological and optical properties respectively. Lowering band gaps of CeVO4‐rGO composites (∼2.15 eV) made the sample active for photodegradation of Bromophenol blue (BRB) and Eosin Yellow (EY) dyes under visible light. Among all, the sample with 20 wt% CeVO4 was the most efficient and almost complete degradation of EY (60 mg/L) was achieved within 60 min with a catalyst dose of 0.4 g/L. In comparison, 91.6 % of BRB dye (20 mg/L) was degraded in 105 min. Recyclability study up to the fourth cycle showed that the composites are fairly stable for reuse.

Efficient peroxymonosulfate activation by CuO-Fe2O3/MXene composite for atrazine degradation: Performance, coexisting matter influence and mechanism

CuO-Fe2O3/MXene was fabricated using a rapid microwave hydrothermal method and used for the enhanced peroxymonosulfate (PMS) activation and atrazine (ATZ) degradation. The ATZ degradation rate could reach up to nearly 100% within 60 min at pH = 6.4, with low dosage for CuO-Fe2O3/5% MXene (0.1 g‧L-1) and PMS (0.37 mM). Experimental results and DFT calculations showed that coexisting matter had little influence on ATZ degradation at low concentrations, indicating the excellent anti-interference capability of the system. Circulation and interaction of ≡Fe(III)/≡Fe(II) and ≡Cu(II)/≡Cu(I) produced SO4•- and •OH, O* and SO5•- could participate in the formation of 1O2. Then, ATZ degradation pathways, including dealkylation, dichlorination-hydroxylation, alkyl hydroxylation, alkyl oxidation, olefination, and deamination-hydroxylation processes, were proposed based on DFT calculations and ESI-QTOF-MS/MS data. QSAR analysis illustrated that most intermediates were more environmentally friendly than ATZ. This study developed novel materials with superior catalytic performance for elimination of refractory organic pollutants in wastewater.

Rapid synthesis and characterization of spinel manganese ferrite nanopowder by microwave-assisted hydrothermal method

Spinel manganese ferrite (MnFe2O4) nanopowder is widely used in many fields, such as the targeted drugs, magnetic fluid sealing technology, magnetic resonance imaging, sewage treatment and so on. The MnFe2O4 nanopowder was synthesized by a rapid microwave hydrothermal method. The phase composition, microstructure and particle size distribution of the as-synthesized nanopowder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and laser particle size analysis, respectively. And their static magnetic properties were measured by vibrating sample magnetometry (VSM). It is found that the microwave hydrothermal reaction time, temperature and the pH of reaction system possess the great effects on the crystallinity, crystallite size and phase composition of the prepared MnFe2O4 nanopowder, and consequently its saturation magnetization (Ms). As the reaction temperature and reaction system pH increase, the average crystallite size of the samples increases gradually, their crystallinities are improved, and the Ms of the prepared nano-MnFe2O4 firstly increase, and then decrease. The MnFe2O4 powder with an average crystallite size of 17 nm and a specific saturation magnetization of 53.6 emu·g−1 was obtained by a microwave-assisted hydrothermal method at a reaction temperature of 130 °C, a reaction system pH of 12 and a reaction time of 10 min. This work provides a rapid and simple approach to prepare MnFe2O4 nanopowder with a high saturation magnetization.

Facile synthesis of Ag2O/ZnO/rGO heterojunction with enhanced photocatalytic activity under simulated solar light: Kinetics and mechanism

Ag2O/ZnO/rGO heterojunction photocatalysts were synthesized via a rapid microwave hydrothermal method for photocatalytic degradation of bisphenol A (BPA) under simulated solar light. Ag doping efficiently decreased the bandgap of ZnO, and loading on rGO inhibited the recombination of photoinduced electron-hole pairs. The highest BPA removal rate (80%) was achieved with an Ag doping ratio of 5% and a GO loading ratio of 3 wt%. The enhanced photocatalytic performance was attributed to the narrower bandgap and the improved separation efficiency of electron-hole pairs. Moreover, the recycling experiments proved that Ag2O/ZnO/rGO possessed excellent photostability. Hole (h+) and •OH played crucial roles in the photocatalytic system. The degradation pathway of BPA including hydroxylation and the cleavage of covalent bonds was proposed. The toxicity assessment of intermediates elucidated that most of intermediates were less toxic than BPA. The as-prepared Ag2O/ZnO/rGO exhibited outstanding photostability and pH adaptability, having great potential to be applied to the degradation of emerging organic pollutants in wastewater.

Visible-light-driven photo-Fenton reactions using Zn1-1.5xFexS/g-C3N4 photocatalyst: Degradation kinetics and mechanisms analysis

The visible-light responsive hybrid catalysts (Zn0.94Fe0.04S/g-C3N4 or ZCN) were synthesized by a rapid microwave hydrothermal method. Our results showed that the deposition of Fe-doped ZnS onto g-C3N4 sheets prevented the aggregation of Zn0.94Fe0.04S and increased the surface area for mass transfer and light absorption. The highest degradation rate of p-nitrophenol (PNP) was 96.0% and the total organic carbon removal rate was 55.4% after 60-min simulated solar light irradiation on ZCN with Fe doping and g-C3N4 loading ratios of 0.04 and 0.20, respectively. Hydroxyl radical played a dominant role in PNP degradation, which was primarily attributed to the photo-Fenton reactions. The PNP degradation pathway involved denitration and hydroxylation reactions according to the Density Function Theory calculations and HPLC-MS/MS results. The QSAR analysis indicated that the toxicity of most intermediates was lower than PNP. This study develops novel materials with superior photocatalytic activity for elimination of refractory organic pollutants in wastewater.

Enhanced brilliant blue FCF adsorption using microwave-hydrothermal synthesized hydroxyapatite nanoparticles

In the present study, hydroxyapatite (HAP) nanoparticles were synthesized by a rapid microwave-hydrothermal method using calcium nitrate tetrahydrate and ammonium hydrogen phosphate as starting materials, and used as adsorbents for the removal of Brilliant blue FCF (BBF). The physicochemical properties of the obtained HAP were characterized by BET surface analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Batch adsorption experiments were performed to investigate the effects of various parameters including initial pH, adsorbent dosage, contact time, temperature, ionic strength, and the presence of humic acid on adsorption efficiency. Results showed that HAP nanoparticles possessed a good ability to adsorb BBF. The adsorption process was fast, and it reached a steady state after only 10 minutes. BBF adsorption increased with an increasing amount of adsorbent dosage but decreased as the pH increased. Increasing ionic strength and the presence of humic acid increased the adsorption of BBF by HAP. The adsorption isotherm studies showed that Sips models could fit the experimental data well, and the maximum adsorption capacity was estimated to be 14.51 mg/g. The thermodynamic parameters suggested that the adsorption of BBF on HAP was spontaneous and endothermic in nature. These experimental results demonstrated that such HAP nanoparticles are promising adsorbents for the efficient removal of BBF dye from water.

Visible-light responsive g-C3N4 coupled with ZnS nanoparticles via a rapid microwave route: Characterization and enhanced photocatalytic activity

Visible-light responsive g-C3N4 catalysts were successfully prepared by the calcination of urea, i.e., the thermal polycondensation method, and a series of ZnS/g-C3N4 composite photocatalysts were then synthesized using a rapid microwave hydrothermal method. The physicochemical properties of the resulting g-C3N4 and ZnS/g-C3N4 catalysts were characterized via several microscopy and spectroscopy techniques. The reduction of Cr(VI) was used to evaluate the photocatalytic performance of the as-synthesized catalysts under visible light irradiation. The results showed that the calcination temperature substantially affected the crystallinity, specific surface area and photocatalytic performance of g-C3N4. The optimal temperature for thermal polycondensation in the g-C3N4 synthesis was 600 °C. The bulk g-C3N4 catalyst exhibited no Cr(VI) reduction ability, while a certain amount of ZnS nanoparticles coupling with g-C3N4 significantly improved the Cr(VI) reduction efficiency, creating a synergistic effect between g-C3N4 and ZnS. The simultaneous Cr(VI) reduction and rhodamine B decolorization by the ZnS/g-C3N4 composite catalyst were also accomplished. In addition, a Cr(VI) reduction mechanism under visible light irradiation was proposed.

Microwave-assisted solvothermal synthesis of novel hierarchical BiOI/rGO composites for efficient photocatalytic degardation of organic pollutants

In the present paper, a novel composite of BiOI/rGO with excellent visible-light photocatalytic activity was successfully fabricated via very different simple, fast and mild rapid microwave hydrothermal method. The BiOI/rGO −1(BG-1) was donated as a simple chemical mechanical and the BiOI/rGO −2(BG-2) was donated as one-step rapid microwave hydrothermal method. The BG-1 were composed of the BiOI microspheres with a diameter of about 1μm and mixed heterogeneously with graphene. While, the BG-2 were consist of the BiOI nanoplates with the thickness of approximately 20nm dispersed heterogeneously on the surface of rGO. The degradation of 40mg/L methylene blue (MB) and 20mg/L levofloxacin (LEV) under visible light irradiation can reach about 11 and 3 times than that of P25, respectively. Furthermore, the reactive species of hole was determined to dominant the photodegradation process. The intensive photocatlytic could ascribe to more effective electron transportation and separations, this conclusion was different with other studies. A possible photocatalytic mechanism of BG-2 was also proposed.

Magnesium whitlockite hollow microspheres: a comparison of microwave-hydrothermal and conventional hydrothermal syntheses using fructose 1,6-bisphosphate, and application in protein adsorption

Magnesium whitlockite hollow microspheres with high biocompatibility and protein adsorption capacity are synthesized by a rapid microwave-hydrothermal method using fructose 1,6-bisphosphate.

P-doped TiO2 with superior visible-light activity prepared by rapid microwave hydrothermal method

Phosphorous-doped anatase TiO2 powders (P-TiO2) were prepared by rapid microwave hydrothermal method. The resulting materials were characterized by XRD, SEM, XPS, DRS and N2 adsorption. P-doping decreased the band gap and enlarged the surface area of P-doped samples than that of undoped TiO2 samples. Therefore, the photocatalytic degradation of methyl blue (MB) and tetracycline hydrochloride (Tc) experiments showed that the P-TiO2 catalysts, especially the two-steps-controlling products P-TiO2-2, exhibited higher degradation efficiency than the undoped TiO2 and commercial P25 under visible-light irradiation. Hydroxyl radicals (OH) have been confirmed to be the active species during the photocatalytic oxidation reaction. The microwave hydrothermal method confirms to be very suitable for the synthesis of superior visible-light activity P-doped samples.

Rapid Microwave Hydrothermal Methods Synthesis of TiO2 Photocatalysts Using Different Sources of Materials

Using TiCl4, Ti(SO4)2 and TBOT as different Ti precursor, titania (TiO2) photocatalysts with high specific surface area were prepared by rapid microwave hydrothermal method. The as-prepared catalysts were characterized by TEM, XRD, DRS and N2 adsorption. The dependence of degradation efficiency of MB on the surface area, crystal structure and band gap of the obtained TiO2 particles were investigated. Results showed that compared with the TiO2 derived from TiCl4 and Ti(SO4)2 precursor, the TiO2 from TBOT exhibited best photocatalytic performance due to its higher surface area, capability of homogenous dispersion and its characteristic of anatanse structure.