Preparation Of Magnesium Based Hydroxide Materials By Wet Chemistry Method And Their Dye Removal Ability From Water

With the rapid development of advanced technology and industry, the living environment of human beings has been heavily destroyed, especially the water resources. A large amount of dyes has been used in industries, such as printing and dyeing industry, paper making, clothing industry, food industry and plastic. The waste effluent from such industries is particularly problematic because of the presence of dyes in final effluent. These organic dyes in wastewater can enter into the surface water or underground water, and finally reach the drinking water system. This can potentially put human health and the living creatures in the water to risk. Thus, it is urgent to develop environmentally friendly, high efficiency and cost-effectively water treatment materials and methods to deal with the dyes in water. Physical adsorption is normally considered as an effective and an economical method because of its high efficiency in removing dyes and easy access in gaining the adsorbents. Since middle of 19 th century, magnesium based hydroxide materials attracts a great interest among researchers, and it was called “Green and safe nature purifying agent”, its destructive sorbent properties, high surface area, and high adsorption capacity makes it to be a very promising material as a physical adsorbent. In this paper, a series of Mg(OH)2 hexagonal nanosheet–graphene oxide composites were synthesized through a simple hydrothermal method and Mg/Al layered double hydroxide(MA LDH) was prepared by a new one step method under mild conditions, and their adsorption performance for dye removing from water was investigated.The GO-Mg(OH)2 composites were synthesized through a hydrothermal method using magnesium nitrate and GO as precursors, sodium nitrate and sodium oxalate as additives, and sodium hydroxide and ammonia as precipitants. Results indicated that GO addition increased the adsorption capacity of Mg(OH)2 and influenced the morphology and BET surface area of Mg(OH)2 nanosheets. The equilibrium adsorption data of CR on the composite were further investigated by Langmuir and Freundlich models, indicating that the Langmuir model was much more suitable for the experimental data. The sample prepared with 0.5 wt% GO showed the highest adsorption capacity with 118 mg·g-1. The experimental data were then fitted using pseudo-second order kinetics, suggesting that pseudo-second order kinetics could well describe the adsorption of CR on composites. Adsorption thermodynamics analysis suggested that the adsorption of CR onto the samples was physical adsorption.A new one step method has been used to prepare Mg/Al layered double hydroxide(Mg/Al LDHs) under mild conditions by using magnesium nitrate and aluminum nitrate as precursors, sodium dodecylbenzenesulfonate(DBS) as additives, and sodium hydroxide as precipitants. The adsorption affinity of the as-prepared samples toward congo red(CR) in water was analyzed and investigated. The equilibrium adsorption data of CR on the materials is well matched with Langmuir models. The experimental data were then fitted using pseudo-second order kinetics, suggesting that pseudo-second order kinetics could well describe the adsorption of CR on composites. Adsorption thermodynamics analysis showed that the adsorption activation energy was 32.9 kJ·mol-1, suggesting that the adsorption of CR onto the samples was physical adsorption. The results showed that Mg/Al LDHs gained a higher adsorption capacity compared to the aluminum hydroxide and magnesium hydroxide, because Mg/Al LDHs has the special layered structure and opposite charges between the layers. The used samples could be simply regenerated by centrifugation and calcination. Moreover, the regenerated samples only showed a slightly decrease in adsorption activity of CR. These findings indicated that Mg/Al LDH was an effective adsorbent for the removal of CR in water.