Removal of Methylene Blue from Industrial Wastewater in Palestine Using Polysiloxane Surface Modified with Bipyrazolic Tripodal Receptor

Different pollutants from industries leach every day to soil and ground waters without treatment. This will lead to different health problems to both human beings and animals. The major problem here is to detect the concentration of one of the pollutants like methylene blue and try to remove it by adsorption. The product N,N-bis(3,5-Dimethylpyrazol-1-ylmethyl)-3-aminopropyl Polysiloxane (Si-C3H6NPz2) was successfully prepared. Fourier Transform Infrared (FT-IR) results confirmed that the Dimethylpyrazole units have been immobilized onto the surface of the modified silica gel. Scanning Electron Microscope (SEM) images of the Modified Polysiloxane surface showed rough and porous nature, indicating that the materials present good characteristics to use as an adsorbent. The adsorption experiments were conducted for a wide range of pH, adsorbent dosage, temperature, initial concentration and contact time. It was observed that the percentage removal of Methylene blue (MB) dye decreased with an increase initial concentration and temperature while it increased with increase in solution pH, contact time and adsorbent dose. Over 70% removal efficiency of MB dye was achieved after 180 min, at solution pH around 10 and 20°C temperature using 0.25 g weight of dose and initial concentration of 15 mg/L of 50 mL MB dye solution. The sorption of MB dye on the (Si-C3H6NPz2) was optimized under alkaline conditions and temperatures around room temperature. MB sorption using (Si-C3H6NPz2) can be described using pseudo second order and Temkin isotherm model. Based on the results, the (Si-C3H6NPz2) is able to remove MB rapidly within 15 min with high removal efficiency. The values amount of MB dye adsorbed per unit mass of (Si-C3H6NPz2) that obtained by Lagergren pseudo second order model, Qe(calc.) was in consistent with the experimental value, Qe(exp.) indicates that the chemisorption might be the rate limiting step where valence forces are involved via electrons sharing or exchange between the adsorbent and the adsorbate. Adsorption behavior of Si-C3H6NPz2 is described by Temkin isotherm, and the results indicate monolayer type exothermic adsorption process involved in the system. The Langmuir maximum adsorption capacity Qm is 11.09 mg/g, at 15°C, and pH 11.83 and 0.04 weight of adsorbent dose. The RL value (0.138 at 15 °C) indicates that the adsorption of MB dye on (Si-C3H6NPz2) is favorable. From Freundlich isotherm model parameters, value of 1/n = 0.6041 while n=1.66 indicating that the sorption of MB dye on (Si-C3H6NPz2) is favorable. The negative ∆G° values (-17.17 to -17.25 KJ/mol) indicate that the adsorption is favorable and spontaneous at these temperatures. The negative value of ∆H° (-16.66 KJ/mol) reflects an exothermic adsorption and indicates that the adsorption is favored at temperature 15oC. The value of ∆H° was higher than those corresponding to physical adsorption. This would suggest that the adsorption process is chemical in nature. The small positive value of ∆S° (+1.78 J/mol.K) suggests that some structural changes occur on the adsorbent and the randomness at the solid/liquid interface in the adsorption system increases during the adsorption process.