Siriluk Chiarakorn

Investigation of CO2 adsorption by bagasse-based activated carbon

Bagasse-based activated carbon (BAC) and amine-modified BAC were prepared and investigated for CO2 adsorption capacity. Modifying BAC with amines resulted in a decrease of surface area, but the decreasing magnitude varied depending on type and loading rate of amines. At room temperature, the unmodified BAC was able to adsorb more CO2 than the amine-modified BAC. This ability was related to the higher surface area of unmodified than that of the modified BAC. When temperature increased, CO2 adsorption capacity of all absorbents was decreased. However, above 323 K and a concentration of CO2 lower than 30% v/v, the BAC modified with PEI at 5 and 25 wt% showed higher adsorption capacity. Among all adsorbents under 15% CO2 and 348 K, BAC-PEI25 showed the highest adsorption capacity (0.20 mmol/g).

Novel Photocatalytic Ag/TiO2 Thin Film on Polyvinyl Chloride for Gaseous BTEX Treatment

This study aims to provide the photocatalytic approach for treatment of some hazard air pollutants such as benzene, toluene, ethylbenzene and xylene (BTEX) under visible light. Silver doped titanium dioxide (Ag/TiO2) thin films with various molar ratios (0.01, 0.05, 0.1 and 0.2 mol) were synthesized via sol-gel method and dipped on polyvinyl chloride (PVC) sheet before curing with UV lamp. The X-ray diffractograms showed the composite of TiO2 anatase and nanosilver. The effect of silver doping on decreasing of band gap energy of TiO2 was observed from the absorption edge shift to higher wave length, analyzed by UV-visible spectrometer. The results from hydrophilicity test indicated that hydrophilicity of TiO2 thin film was increased by doping silver. The morphology of the Ag/TiO2 thin film studied by Scanning Electron Microscope equipped with an Energy Dispersive Spectrometer revealed well dispersed nanosilver on the smooth thin film. The BTEX degradation was carried out in a batch reactor with the initial concentration of mixed BTEX gas [25 ppm]. The remaining BTEX was examined by Gas Chromatography equipped with flame ionization detector. Among Ag/TiO2 thin films, the 0.1 Ag/TiO2 thin films exhibited the best performance for gaseous BTEX degradation under visible light. The maximum degradation efficiency was belong to xylene (89%), followed by ethylbenzene (86%), toluene (83%) and benzene (79%).

Enhancement of elemental mercury adsorption by silver supported material

Mercury, generally found in natural gas, is extremely hazardous. Although average mercury levels are relatively low, they are further reduced to comply with future mercury regulations, which are stringent in order to avoid releasing to the environment. Herein, vapor mercury adsorption was therefore investigated using two kinds of supports, granular activated carbon (GAC) and titanium dioxide (TiO2). Both supports were impregnated by silver (5 and 15 wt.%), before testing against a commercial adsorbent (sulfur-impregnated activated carbon, SAC). The adsorption isotherm, kinetics, and its thermodynamics of mercury adsorption were reported. The results revealed that Langmuir isotherm provided a better fit to the experimental data. Pseudo second-order was applicable to describe adsorption kinetics. The higher uniform Ag dispersion was a key factor for the higher mercury uptake. TiO2 supported silver adsorbent showed higher mercury adsorption than the commercial one by approximately 2 times. Chemisorption of mercury onto silver active sites was confirmed by an amalgam formation found in the spent adsorbents.

Enhancement of Photocatalytic Activity of TiO2 Thin Film Using Diethanolamine and MCM-41

TiO2 thin film enhanced by diethanolamine (DEA) and MCM-41 (D-TiO2/MCM-41) was successfully synthesized by sol-gel dip coating technique on glass slides. The roles of DEA and MCM-41 on physical and photocatalytic characteristics of the films were studied using various techniques such as x-ray defraction (XRD), fourier transform infrared spectroscopy (FTIR), ultra violet-visible (UV-Vis) spectrometry, Brunauer, Emmett and Teller (BET) surface area analysis and field emission scanning electron microscope (FESEM). The XRD results showed that the thin film contained almost 100% anatase phase and the crystal size of TiO2 was in the range of 4-8 nm. The FTIR spectra indicated the formation of Ti-O-Si and Si-O-Si linkages due to interaction of TiO2 and MCM-41. The surface area of TiO2 was increased significantly when MCM-41 was added. The use DEA and MCM-41 caused slight increase in visible light absorption but UV absorption was decreased. The photocatalytic reactivity of the thin film was tested by photocatalytic degradation of methylene blue under visible light. The addition of DEA as a nitrogen source was beneficial not only for obtaining stable/smooth surface of the thin film but also for enhancing photocatalysis of methylene blue by preventing charge carrier recombination. While MCM-41 played important functions in improving porosity and hydrophilicity of the film. The photodegradation of methylene blue was obtained up to 35% of its original concentration when 1M DEA and 0.3M MCM-41 were incorporated in TiO2 thin film. The overall enhancement of photocatalytic activity of the film was a result of nitrogen doping, increased surface area as well as increased hydrophilicity provided by MCM-41.

Inducing Catalytic Activity in the Dark of TiO2/WO3 Mixed Metal Oxides by Using an In Situ Polymerized Semiconductive Polymeric Binder

Mixed metal oxides (TiO2/WO3) containing polythiophene binder were prepared. The molar ratios of TiO2/WO3/thiophene used for an in situ polymerization were varied from 1/2/0 to 1/2/0.6. Catalytic activities of the metal oxides were studied by following up the degradation of methylene blue under various illumination conditions. With the presence of the polymeric binder in the system, the activity in the dark was induced whereas those under both UV and visible light were maintained. The amount of polymer also played a role. The catalytic activities decreased with increasing monomer content. The results are discussed in light of morphology characterized by TEM-EDX.

Improvement of BTEX Adsorption Using Silylated RH-MCM-41 Synthesized from Rice Husk Silica

RH-MCM-41, a mesoporous molecular sieve, was successfully synthesized from silica extracted from rice husk. The presence of silanol functional group (Si-OH) on its surface causes adverse effects on the adsorption of some non-polar compounds, especially benzene, toluene, ethylbenzene and xylene (BTEX). Thus, this work aims to enhance the adsorbability of RH-MCM-41 on BTEX adsorption by in-situ and ex-situ silylation. Trimethylchlorosilane (TMCS) was used as a silylating reagent to reduce silanol groups. The ex-situ silylation was carried out by adding as-synthesized RH-MCM-41 into 5% v/v of TMCS solution at 30°C and stirring for 24 h. While the in-situ silylated sample was prepared by mixing 5% v/v of TMCS solution and RH-MCM-41 precursor solution at 80°C and stirring for 120 h. The adsorption capacity of gaseous BTEX using the silylated RH-MCM-41 was determined by gas chromatography equipped with a flame ionization detector (GC-FID) with a thermal desorption unit (TDU). The adsorption capacities of the ex-situ samples were 0.617 mg g-1 for benzene, 1.271 mg g-1 for toluene, 1.902 mg g-1 for ethylbenzene and 0.036 mg g-1 of xylene, higher than that of the in-situ and the unsilylated samples. Thus, the ex-situ silylation is suitable for enhancement of hydrophobicity of RH-MCM-41. The ex-situ silylated RH-MCM-41 has the potential to be applied in gaseous BTEX treatment.