Utilization of inorganic porous materials for the removal of dyes from aqueous media

Abstract

Being a visible contaminant, dye presence in aqueous media make it unfit for drinking use. Various efforts to treat this type of contamination are being done now a days. Use of some heat stable adsorbents is an appropriate and safe method to uptake colorant particles. Synthetic inorganic porous polymers like silica and titania are best to remove cationic particles of basic dyes. Practical efforts have been done using such simple materials and their composites. The whole phenomenon was optimized using quantitative parameters like temperature, dye molecule concentration, amount of added adsorbent, equilibrium time required and concentration of hydrogen ions etc. Points of zero charge for MPS, MPT, MPST, MPSF and MPS-NH2 were 2.4, 6.2, 5.6, 6.3 and 7.6 respectively. Optimum value of pH was observed in range of 7 to 8 for adsorption of all dyes by MPS and MPST with qe value upto 46 mg/g. These two adsorbent showed the highest adsorption capacities at optimum pH. Optimum time for Basic Blue XGRRL 250 was 90 min with adsorption capacity 45.3 and 47.3 by MPS and MPST. Equilibrium was achieved for Golden yellow, Red-3R and T-blue at 90 min, 60 to 90 min and 90 min using MPS and MPST as adsorbents. Highest adsorption capacities were in range of 43 to 47 mg/g for these dyes using both adsorbents. Optimum dose of all adsorbents for adsorption of all dyes was 25 mg. However, qe values were different i.e. 71, 65, 74, 57, 27 mg/g for MPS, MPT, MPST, MPSF and MPS-NH2, respectively. In adsorption of Blue-XXRGL. In case of Golden yellow, Red-3R and T-blue highest qe values were 62 mg/g for MPS, 69 mg/g for MPST and 68 mg/g for MPST. Highest adsorption capacities at 300 mg/g concentration of all dye solutions were 93 and 88 mg/g for MPS and MPST in case of Blue-XXRGL. For Golden yellow, Red-3R and T-blue, at concentration of 300 mg/L, the highest qe values were 83, 90 and 93 mg/g for MPS and 87, 88 and 90 mg/g for MPST composite. As adsorption of all dyes was exothermic so maximum qe values were observed at 303 K for all dyes. Presence of CTAB surfactant decreased adsorption capacities of all adsorbents. It was most significant for MPS and MPST. In presence of Mg(NO3), Mg ion decreased qe values due to its high charge density and competition with dye molecules. Adsorption capacities by MPS and MPST were observed 24.3 and 25.5 mg/g, 24.3 and 21.6 mg/g, 24.5 and 21.3 mg/g and 26.5 and 19.6 mg/g for Blue-XXRGL, Golden yellow, Red-3R and T-blue respectively. Adsorption capacities of other adsorbents were also decreased in range of 20 to 25 mg/g. RSM analysis told about interaction of levels of two factors. Langmuir equilibrium model was found best as with highest coefficient of determination among all other models. Similarly pseudo second order kinetic equation explained better the phenomenon in case of almost all time variation based experiments. Spontaneity of process was predicted by finding the values of thermodynamic parameters like enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG). Characterization of materials was done by SEM, EDX, XRD, FTIR, BET and BJH analysis to study surface morphology, crystalinity, functional sites, surface area and pore diameter. All experimental values were noted three times and shown with standard deviation.