Adsorption is a well-established unit operation in chemical process industries utilizing variety of adsorbents having varied adsorption characteristics. The present work attempts to utilize date palms pits as a suitable precursor for preparation of porous carbons with phosphoric acid as an activating agent. The experimental methods reported in literature were synthesized and an appropriate method was chosen to simplify the process. The process optimization was performed using the popular Response Surface Methodology (RSM) adopting a Box-Benkhen design, involving three independent optimizations. In the first case, process optimization was performed to maximize the activated carbon (AC) yield and the methylene blue (MB) adsorption capacity, while in the second case the objective was to maximize the yield and BET surface area with the process variables being activation temperature, activation time and impregnation ratio.
The AC samples were characterized using nitrogen adsorption isotherms for the estimation of BET surface area, pore sizes and distribution of pores, Scanning Electron Microscope (SEM), Fourier Transform Infrared (FT-IR), while the adsorption capacity was estimated using the methylene blue (MB) adsorption tests. The optimized experimental conditions for maximizing the yield and MB adsorption capacity was identified to be an activation temperature of 400o°C, Impregnation ratio (IR) of 3 and activation time of 58 min, with the resultant AC yield of 44% and MB adsorption capacity of 345 mg/g. The textural characteristics of the AC reveal the BET surface area to be 725 m2/g, with pore volume of 1.26 cc/g and an average pore diameter of 2.91 nm. The MB adsorption isotherms were experimentally generated and were tested with the popular Langmuir and Freundlich adsorption isotherm models, to identify the model that match with the experimental data. The maximum monolayer adsorption capacity of the MB was estimated to be 455 mg/g, which compares with the highest of MB reported in literature, evidencing the suitability of the AC for adsorption of macro molecular compounds. The kinetics of methylene blue (MB) adsorption was assessed by varying the initial concentration and the adsorption temperature. The kinetic parameters were evaluated applying different kinetic models by minimizing the error between the experimental data and the model prediction. Among the models tested a pseudo second order model and Elovich's model were found to represent the experimental data more aptly.
The optimum conditions for maximizing the yield and BET surface area was identified to be an activation temperature of 500 °C, impregnation ratio (IR) of 2 and activation time of 75 minutes with the resulting yield and BET surface area of 46 % and 838 m2/g. The pore volume and pore diameter of the optimized sample was estimated to be 1.07 cc/g and 1.69 nm respectively. The low activation temperature, activation time with highest of yield renders the above process technically/economically attractive for commercial manufacture.
Sulfur impregnated carbons are being widely used in gas processing industry for removal of mercury. The process of preparation of sulfur impregnated carbons was found to vary widely adopting different experimental techniques and conditions. In order to identify optimum process conditions for maximizing the adsorption of mercury, process optimization was performed with the process variables being impregnation temperature, impregnation
Optically transparent semiconductor surfaces of indium tin oxide (ITO) were used as the adlayer for EA-TIRF and EA-IOW devices. The ITO surface morphology, optical and conduction properties were characterized. The ITO was found to have adequate conduction, optical and surface morphology properties for molecular orientation distribution measurements. The results indicated the ITO morphology contributes a minimal degree of error to the calculated distribution.
Surface-bound films of model methylene blue were used to characterize the EA-TIRF and EA-IOW techniques prior to the investigation of horse heart cytochrome c. The studies demonstrated potential control of redox active adsorbed films. The mean tilt angle and the angular distribution about that mean were successfully determined. In addition, the studies of the methylene blue films indicated the possibility of orientation-dependent quenching (the loss of an electron from the excited state LUMO to the ITO semiconductor conduction band).
Studies of the cytochrome c films indicated anisotropic submonolayers electrostatically bound to the negative ITO surface. Cyclic voltammetry measurements showed the films to be electroactive, exhibiting quasi-reversible electrochemistry. An average tilt angle and the orientation distribution about the angle, as a function of potential, were reported for horse heart cytochrome c. This potential-dependent orientation distribution of submonolayer films is reported for the first time.