Using Thiophene Supported on SiO2 for Removal Cr(VI) from Water

Water pollution is a major environmental problem especially that produced from different industries, which produce large amounts of toxic heavy metals to the soil and wastewater; these heavy metals affect human health. This study was made to study the removal of one of these toxic heavy metals which is Cr(VI) by adsorption technique using silica gel compound 3-Glycidoxypropyl- functionalized silica. The compound 3-Glycidoxypropyl- functionalized silica (MSiTh) was successfully prepared and characterized, studying the attachment of thiophene group to silica FTIR was used. Thermogravimetric analysis for MSiTh, and the average BJH pore diameter were made. The adsorption experiments were applied for a range of pH (2-13), temperature, adsorbent dosage, initial concentration, and contact time. The results revcaled that the percentage removal of Cr(VI) decreased with the increase of Cr(VI) concentration, pH and temperature, while the percentage removal increase with increase contact time and adsorbent dose. The removal efficiency for Cr(VI) adsorption was more than 75% after 24 hour this achieved at pH around 6, and temperature 25ºC, using 0.04g weight of dose, at initial concentration 10 ppm for 10 mL Cr(VI) solution. The adsorption of Cr(VI) onto MSiTh was optimized under acidic conditions (pH< 7) at room temperature. According to pseudo second order the Cr(VI) sorption, the results achieved shows the MSiTh is able to remove Cr(VI)within 20 min with high removal efficiency. The amount of Cr(VI)adsorbed per unit mass of MSiTh that obtained by Lagergren pseudo second order model, q(cal) has been agreed with experimental value of q(exp) indicates that exchange between the adsorbent and adsorbate . The Langmuir maximum adsorption capacity Qm is 10.672 mg/g, at 25ºC, pH around 6, and0.04g weight of adsorbent dose .the RL value (0.2375 at 25ºC) indicates the adsorption of Cr(VI)onto MSiTh is favorable. From Freundlich isotherm model parameters, value of 1/n = 0.56, while n=1.786, indicating that the sorption of Cr(VI)is favorable. The negative ΔG° values (- 1.01443 – 0.92983 KJ/mol) indicate the adsorption is favorable and spontaneous at temperatures in the experiment. The negative value of ΔH° (- 1.62355KJ/mol) shows an exothermic adsorption process and indicates the adsorption is favorable at 25ºC. the positive value of ΔS° = 2.115J/mol.K indicates some randomness at the solid/liquid interface in the adsorption system which increase the adsorption process.