Studies on Polymer Nanocomposite Adsorbents for Dye Removal

Abstract

In the current century, wastewater treatment is a worldwide challenge. Every year, a large amount of wastewater is generated from cosmetics, plastics, paper, leather, rubber, printing, food, and pharmaceutical and textile industries. The textile dye pollutant water is highly toxic and is one of the major reasons for the environmental problems. The harmful chemicals present in the dyes create an adverse effect on human lives. India's textile sector alone generates about 60,000 metric tonnes of dyes. Many different methods have been used to treat such contaminated wastewater. These methods are adsorption, reverse osmosis, membrane filtration, electrodialysis, ion exchange, coagulation, chemical precipitation, flocculation, biodegradation, etc. but adsorption is one of the most cost-effective and efficient methods for removing dyes from wastewater. Many researchers have studied different types of adsorbents to remove dye effluent successfully, and activated carbon is the most popular one, but the operational cost of activated carbon is very high. Thus, there is a need to develop a low-cost and economical adsorbent with a higher surface area and higher adsorption rate. Nanotechnology provides the opportunity for researchers to treat wastewater effectively. Polymer nanocomposites material with improved physical properties plays an important role in higher textile wastewater treatment. In the present work, we have synthesized high surface area nanocomposites through an in-situ polymerization process of aniline, using HCl as a catalyst and ammonium persulfate as an oxidizing agent. A probe sonicator has been used for nanodispersion of clays and CA powder. Micron-sized colloidal particle aggregates are broken down to the nanoscale level using a probe sonicator. Prior to sonication, a homogenizer was used to make a homogeneous suspension. The different synthesis processing routes were studied. Further, the pure CA and prepared PANI, PANI/MMT, and PANI/CA nanocomposites were utilized as adsorbents for adsorption of Acid green 25 and Methylene blue dye in a batch process. Acid green 25 (anionic) and Methylene blue (cationic) dyes are highly soluble in water and at the same time, highly poisonous in nature. Thus, elimination of textile dyes is essential before being discarded in the environment. The present work focuses on the treatment of these two harmful dyes by using nanocomposite adsorbents. Although PANI/MMT nanocomposites have already been utilized as adsorbent to treat wastewater, no research has been done on adsorption of Acid green 25 using PANI/MMT nanocomposites adsorbent. For MB adsorption, only a single study has been reported. Carbon aerogels have not been researched much in the past but lately because of their highly porous nature, it is attracting a lot of interest. Only a few studies are there on the synthesis of carbon aerogel/polyaniline nanocomposites material. There is a lack of study on the adsorption process through carbon aerogel-based adsorbents. Moreover, no research on AG25 dye adsorption with PANI/CA nanocomposites has been reported so far. Adsorption study of Acid green and Methylene blue has been performed in a batch mode. The entire adsorption study was done by involving different parameters i.e. pH, initial dye concentration, time, adsorbent loading, and temperature. In the adsorption study results of Acid green 25 dye onto PANI and PANI/MMT adsorbents, adsorbent dosage = 0.4 g, pH = 6, and contact period 30 minutes were determined to be optimal adsorption conditions. Complete removal of Acid Green 25 dye (AG25) was achieved with PANI/MMT nanocomposite adsorbent and 99.16% with pure PANI sample. The adsorption results onto PANI/MMT were superior to pure PANI. The pseudo-second order model performed well for adsorption kinetics. Langmuir model best describes adsorption thermodynamic properties. An adsorption study was also performed with CA and PANI/CA adsorbent. The optimum parameters of this study were found to be pH = 7, adsorbent dose = 0.1 g for CA and 0.4 g for PANI/CA, time 0-30 min for CA, and 0-60 min for PANI/CA. Furthermore, the results of CA show better dye removal as compared to PANI/CA adsorbent. The effect of the initial AG25 dye concentration showed that the lower dye concentration is more favorable to remove more dye. The kinetics of AG25 onto CA and PANI/CA have been well described using the pseudo-second-order model. The highest correlation coefficient (R2= 1) values were achieved with the CA adsorbent. Two models, Langmuir and Freundlich, provided the best data fit of AG25 onto CA. The Langmuir model best suited the data for PANI/CA, implying monolayer adsorption. On pure CA adsorbent, the maximum adsorption rate of 518 mg/g was achieved. Methylene blue dye adsorption has been done on PANI and PANI/MMT adsorbent. PANI/MMT adsorbent shows better results as compared to pure PANI adsorbent. With a rise in the pH of the MB dye solution, the percentage adsorption of dye onto PANI was increasing. For PANI/MMT adsorbent, the maximum removal was attained at neutral pH. The kinetic study was performed with pseudo-first and second-order models. The pseudo-second-order model best represented it. MB adsorption isotherm best fits the Temkin model for PANI adsorbent and the Langmuir model for PANI/MMT adsorbent. In this study, the prepared adsorbent material gave excellent adsorption results, and this is because of the different processing routes that have been used to prepare nanocomposites. Essentially, the key is in nano-dispersion of clay and CA. Acid green 25 and Methylene blue adsorbed at a very fast rate, at least by a factor of 20, as compared to earlier studies onto PANI and its nanocomposite adsorbents. Therefore it will be a great material for textile wastewater treatment. The synthesized materials have the potential to treat textile wastewater efficiently.