Adsorption Of Aqueous Cr⁶⁺ Ions By Mesoporous Carbons With And Without Modification

Removal of toxic chromium from water and wastewater is obligatory in order to avoid water pollution. Among various sorbents for removing aqueous chromium ions, the porous carbon materials are more versatile and effective sorbents due to their high sorption capacity, fast sorption rate, chemical inert, low-cost and easy-to-use. In this thesis, mesoporous carbon materials and their derivants (Fe3O4loading, sulfur loading and nitrogen doping) were used to adsorb Cr6+in aqueous water. The main results are summarized as follows.(1) Mesoporous carbon microspheres (MCS) have been prepared by a facile and scaleable spary dring method. The obtained MCS have been used as the chromium adsorbent with considerable adsorption capacity and good regenration ability. The pH value has a great effect on aqueous chromium removal, and the adsorption capacity reach the maximum value at pH3.0. The chromium adsorption active sites are mainly located in the micropores, thus the MCS with larger surface area and greater pore volume exhibit higher chromium adsorption capacity. The maximum saturated adsorption capacity of MCS is160.2mg/g. The adsorption process will reach equilibrium at24h, and the adsorption kinetics fit well with pseudo-second-order kinetic model. The adsorption isotherm fit well with both Langmuir and Frundlich models. The thermodynamic parameters indicate that the adsorption is an endothermic process, which is contorlled by both physical adsorption and chemisorption. The adsorption capacity of MCS after5cycles is120.9mg/g, approximately80%of the initial one.(2) The Fe3O4loaded MCS can greatly reduce the cost of the seperation process by using magnetic separation technology. Moreover, the weight loss of the adsorbent during the regeneration can be reduced by using magnetic separation. Similar to the prestine MCS, the Fe3O4loaded MCS still show favorable adsorption performenace in the acidic conditions. The adsorption equilibrium can be achieved in24h, while the adsorption capacity slightly reduces compared to the unmodified MCS, due to the addition of Fe3O4.(3) The introduction of elemental sulfur into MCS can accelerate adsorprtion rate and shorten the equilibrium time. The kinetic rate constant of C-10-10%S can be improved about3-fold after sulfur loading. However, the sulfur loading can block some micropores, resulting in the decrease of active microporous BET surface area and micropore volume. Thus, the kinetic improvement is balanced by the reduction of adsorption capapctiy.(4) The nitrogen atom doping in the carbon framework can introduce basic properties into the MCS, thus facilitating the adsorption of aqueous Cr6+. The equilibrium time can be shorten within20h, while the adsorption kinetics still fit well with the pseudo-second-order model. The total adsorption capacity generally increases with the increase of the nitrogen content.