Synthesis of zeolite from coal fly ash by hydrothermal method without adding alumina and silica sources: effect of aging temperature and time

The aim of this research was to synthesize zeolite from coal fly ash by hydrothermal method. The effect of aging temperature and time on zeolite P1 synthesis (Na-P1) from Mae Moh coal fly ash (MFA) without adding any alumina and silica sources were examined during the synthesized process. The central composite design (CCD) was used for experimental design to obtain the optimal process parameters of the aging temperature (105-195ºC) and time (12-84 h) where the specific surface area was used as a response. The chemical and physical properties of Na-P1 such as specific surface area, crystalline phase, compositions and morphology were examined. The response results showed that the specific surface area of Na-P1 decreased with an increase of both aging temperature and time, whereas the XRD intensity of Na-P1 increased with an increase of both aging temperature and time. The composition of SiO2/Al2O3 in mass ratio of coal fly ash was observed, which was suitable to Na-P1 synthesis. The maximum specific surface area of zeolite products was found at the designed condition of aging temperature of 105ºC and time of 12 h. Thus, zeolite P1 can be prepared by hydrothermal method without adding any alumina and silica sources

Lead adsorption behaviours on nanoscale zero valent irons (nZVI) coupled with rice husk MCM-41

The aims of this work were to investigate the characteristics of nanoscale zero valent irons (nZVI) coupled with mesoporous materials (RH-MCM-41) adsorbent and to study the removal mechanisms of Pb (II) from synthetical solutions using full pictorial design batch experiments. Synthetic nZVI coupled with RH MCM-41 as Pb (II) adsorbent were characterized by XRD, TEM, BET and XANES. The results of XANES analyses confirmed the ability of RH-MCM-41 to prevent oxidations of Fe0 to Fe2+ and Fe3+. XANES results also verified the oxidation states of Pb (II). The solution pH was the most significant positive effect in controlling Pb (II) adsorption. The equilibrium and kinetic adsorption isotherms well fitted with the Langmuir isotherm. The pseudo-second order kinetic adsorption indicated that the adsorption process is the rate limiting step for Pb (II) removal. Furthermore, Langmuir-Hinshelwood confirmed the obvious Pb (II) adsorption at the active site of adsorbents. The reduction rate constant (kr = 5,000 mg/L.min) was higher than the adsorption rate constant (Kad = 0.0002 L/mg). Regarding the research results, four pathways including: reduction process, adsorption on FeOOH, adsorption on RH-MCM-41 and complex reaction between Fe and Pb ions were suggested for Pb (II) removal by nZVI coupled with RH-MCM-41

Gas phase catalytic oxidation of VOCS using hydrothermally synthesized nest-like K-OMS 2 catalyst

Toluene and benzene are hazardous air pollutants commonly found in the atmosphere at relatively high concentrations. Due to this, a need to remove these pollutants became a necessity. In this study, octahedral molecular sieve type manganese oxide (K-OMS 2) prepared by hydrothermal method was utilized to decompose toluene and benzene. X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmet-Teller (BET), X-ray absorption near edge structure (XANES) analysis were used to investigate the crystallinity, morphology, surface area and oxidation state of K-OMS 2, respectively. It was confirmed that K-OMS 2 was successfully produced from hydrothermal method. Central composite design (CCD) was used to investigate the main and interaction effects of gas hourly space velocity (GHSV) and reaction temperature on the thermal catalytic oxidation of benzene and toluene. Both factors were found to have significant main and interaction effects on toluene oxidation. However, only the main effects of the factors were significant for benzene. This result was due to the difference in the stability of the structures of the two VOCs. The K-OMS 2 obtained has excellent efficiency on toluene and benzene removal. Toluene was completely decomposed at a temperature as low as 250°C while benzene decomposition reached around 98% at 292.4°C

Optimization for UV-photocatalytic degradation of paraquat over titanium dioxide supported on rice husk silica using Box-Behnken design

363-371The optimum conditions for UV-photocatalytic degradation of paraquat over titanium dioxide supported on rice husk silica (TiO2/RH-SiO2) catalyst, which is effected by four independent variables, namely initial paraquat concentration, pH of solution, titanium dioxide content (% TiO2) and catalyst loading,  have been evaluated. The TiO2/RH-SiO2 catalyst has been synthesized by colloidal impregnation method and calcined at 550 °C for 6 h. The Box-Behnken design, based on response surface methodology has been applied to design the experiment and analyze the data. Characterization of the catalysts is investigated by XRD, SEM, BET surface area and UV-DRS for explanation of reaction behaviour. The XRD patterns show a pure anatase crystalline phase at all TiO2 percentages, and the BET surface area of the catalysts is vastly decreased as the percentage of TiO2 is increased. The highest paraquat removal efficiency of 90.04% is obtained at 10 ppm initial paraquat concentration, 5.91 pH, 30 wt % TiO2 and 2.0 g/L catalyst loading

Photocatalytic transfer of aqueous nitrogen into ammonia using nickel-titanium-layered double hydroxide.

The development of solar-driven transfer of atmospheric nitrogen into ammonia is one of the green and sustainable strategies in industrial ammonia production. Nickel-titanium-layered double hydroxide (NiTi-LDH) was synthesised using the soft-chemical process for atmospheric nitrogen fixation application under photocatalysis in an aqueous system. NiTi-LDH was investigated using advanced characterisation techniques and confirmed the potential oxygen vacancies and/or surface defects owing to better photocatalytic activity under the solar spectrum. It also exhibited a bandgap of 2.8 eV that revealed its promising visible-light catalytic activities. A maximum of 33.52 µmol L-1 aqueous NH3 was obtained by continuous nitrogen (99.9% purity) supply into the photoreactor under an LED light source. Atmospheric nitrogen supply (≈78%) yielded 14.67 µmol L-1 aqueous NH3 within 60 min but gradually reduced to 3.6 µmol L-1 at 330 min. Interestingly, in weak acidic pH, 20.90 µmol L-1 NH3 was produced compared to 11.51 µmol L-1 NH3 in basic pH. The application of NiTi-LDH for visible-light harvesting capability and photoreduction of atmospheric N2 into NH3 thereby opens a new horizon of eco-friendly NH3 production using natural sunlight as alternative driving energy