Study Of ZnO/Activated Carbon Fibers Composites

ZnO photocatalysis is an energy-saved and high efficiency green environmental technology. It has the advantage of a high chemical stability, low cost, strong oxidation and good degradation. ZnO photocatalyst has an attractive application perspective in waste water treatment and air purification. Nano-ZnO is considered a very promising highly active photocatalyst, which can break down organic material, anti-bacterial and deodorant under UV irradiation. Currently, as photocatalyst, ZnO was used in wastewater treatment by photocatalytic degradation. There are two main forms for ZnO photocatalyst, one is direct using of ZnO powder suspension, and the other is immobilizing ZnO photocatalyst onto substrates. Suspended nano-ZnO was with high surface area, but easy to gather together, easy to be poisoned, difficult to recycle and low utilization of sunlight. Bulk or ball ZnO was with poor adsorption, as a result, it takes a long time to achieve complete degradation of organic matter, which greatly limits the application of photocatalytic oxidation technology in production. So, it is very important to immobilize the ZnO photocatalyst onto substrates to improve its photocatalytic efficiency.The strong adsorption properties of activated carbon can provide high concentrations of ZnO photocatalytic reaction of organic pollutants in the environment. The combination of activated carbon adsorption and photocatalytic activity of ZnO, which makes supported nano-ZnO maintain same high photocatalytic activity and has good nature of settlement and separation for recycling the catalyst. It provides favorable conditions for the purification of wastewater treatment and explores new methods to improve the efficiency of ZnO photocatalytic degradation. The environment of high concentrations accelerated the photocatalytic degradation of pollutants in photocatalytic reaction rate. It enhanced the photocatalytic activity through diffusion and decomposition of the adsorption of organic pollutants on the carrier. The activated carbon prices are relatively low, so as to promote the industrialization of photocatalytic technology. Activated carbon fiber (ACF) is based on the development of combination of activated carbon fiber technology and activated carbon technology. It is the third generation of activated carbon products following powdered and granular activated carbon, which has excellent absorption properties and adsorption capacity. We selected paper as precursor of activated carbon fiber in this work and paper activated carbon fibers were prepared by physical activation with CO₂ and chemical activation with KOH. SEM results indicated the activated carbon fibers exhibited fiber structure with lots of micropores. XRD reveals that paper carbons are mainly amorphous after carbonization and activation. The surface area of 1517 m²/g and 1474 m²/g were obtained at 880℃with CO₂ activation for 2 hours and 3 hours, respectively. Activated carbon fibers (ACFS) with surface area of 1388 m²/g prepared from paper by chemical activation with KOH has been utilized as the adsorbent for the removal of methylene blue from aqueous solution. The effect of activated time on specific surface area of ACFS was also studied. The experimental data were analyzed by Langmuir and Freundlich models of adsorption. The effects of pH value on the adsorption capacity of ACFS were also investigated. The rates of adsorption were found to conform to the kinetic model of Pseudo-second-order equation with high values of the correlation coefficients (R>0.998). The Langmuir isotherm was found to fit the experimental data better than the Feundlich isotherm over the whole concentration range. Maximum adsorption capacity of 520 mg/g at equilibrium was achieved. It was found that pH played a major role in the adsorption process, higher pH value favored the adsorption of MB.ACFS was soaked in Zn(NO3)2 .6H2O solution. After drying, the samples were then calcined at 500, 600, 700, and 800℃for 1 h, respectively to get ZnO/ACFS composites. The effect of ZnO loading amount and calcined temperature on the photocatalytic degradation of ZnO/ACFS composite was studied. It was found that ZnO/80% ACFS (ZnO loading was 20%) with best photocatalytic degradation effect at the calcined temperature of 700℃. After 120min ultraviolet light exposure, the degradation rate was 99% or more, almost complete degradation of methylene blue.