Synthesis of a new nanocomposite with the core TiO2/hydrogel: Brilliant green dye adsorption, isotherms, kinetics, and DFT studies
Introduction
Hydrogels are water-swellable cross-linked polymers. They have a high ability to absorb water and maybe the highest amount of one thousand times the polymer weight. Hydrogels are widely applied and examined due to the mixture of glassy and elastic behavior. Moreover, researchers employed them in industries like pharmacy, agriculture, biotechnology medicine, food production, and biotechnology. In general, they are mainly utilized to control the drug releases, and their physico-chemical features depend on the monomers, cross-linker, and polymers where they have been constructed. In addition, they contain diverse chemical materials [1].
The molecules of dye contain two main elements; chromophores that involve the production of color and auxochromes that may complement chromophores, and the water-soluble molecules, resulting in greater affinity for attaching with the fibers [2]. These dyes exhibited remarkably diverse structures and have been categorized in different methods. They may be grouped via their chemical structures, kinds of fibers [3], and based on solubility.
The soluble dyes contain mordant, acid, metal complex, basic, and reactive dyes. While the insoluble dyes contain azoic, disperse, and vat sulfur dyes. It is worth to be mentioned that the azo dyes have extensive uses and account for 65% to 70% of the total created dyes. In addition, synthetic dyes have mainly been utilized in several sectors of the textile industry including printing paper, leather, plastic, drug, color photography, and cosmetics [4], [5]. But unfortunately, discharge of the industrial wastewater containing dyes causes acute ecological issues since it has significant toxicity and probably is accumulated in the environment [6].
Moreover, synthetic dyes have been introduced as groups with the highest degree of detrimental contaminants in water [7], [8]. Additionally, the presence of little dyes concentration in aquatic reduces the light penetration through the water surface, preventing the aqueous flora's photo-synthesis. Several dyes have been identified as carcinogenic, teratogenic, and mutagenic that are too toxic for humans, micro-organisms, and different fish species. For this reason, the elimination of such dyes from aquatic wastewater is ecologically significant [9], [10], [11].
One of the important methods used for treating many pollutants in water and wastewater is the adsorption using different materials. Fazlzadeh and co-workers used an activated carbon coated by nanoparticles ZnO and nZVI derived from pomegranate peel extracts. The new adsorbent was applied in the removal of cephalexin from aqueous solutions [12]. Azari et al. have been synthesized a novel silica- chitosan-glutaraldehyde adsorbent and they used for extraction of Penicillin G (PG) from the synthetic and real samples. Also, they have been applied it successfully for determination of PG in real water samples and wastewater samples [13]. The bioadsorbent Enterolobium contortisiliquum was also used, which enhanced the removal of cationic dyes in the purification of contaminated effluents [14]. Recently, a new series of hybrid GrO/MIL-101(Cr) (GrO@MCr) nanocomposites were prepared via hydrothermal synthesis. The synthesized composites were applied in the removal of the organic pollutants methyl orange (MO) and reactive blue 198 (RB198) from an aqueous solution [15]. More recent, the surface of polyacrylamide cryogels (PAC) was modified with ZnO nanorods (ZNR) to provide it with antibacterial properties. The modified composite showed very high potential both in the removal of dyes from the wastewater and in the purification of microorganism-contaminated water [16].
Regarding the adsorption studies related to the removal of brilliant green dye, there are different studies that involved different adsorbents at different conditions. Jaspal and co-workers reported the column studies for the adsorption of brilliant green using waste materials like bottom ash (BA) and de-oiled soya as adsorbents, which were found useful for the elimination of the dye [17]. Popoola et al. reported the successful use of low-cost composite snail shell–rice husk, which proved to be valuable for the removal of the BG dye from an aqueous solution [18]. Areca nut husk which is an agricultural by-product also used, after modification with sodium hydroxide, as an inexpensive and effective adsorbent for removal of the dye in an aqueous solution [19]. Last but not least, Lignite loaded with azospirillum bacteria as a bio-adsorbent was used for the removal of Brilliant Green dye in a fixed-bed adsorption column. The results predicted that the column adsorption system above is effective [20].
In the current study, new SA-g-P(AAc-co-MA)/TiO2 nanocomposite was synthesized and utilized as an adsorbent to remove Brilliant green (BG) dye from the aqueous solution. The new adsorbent showed efficient adsorption at the optimized condition used in work. Last but not least, to supplement the experimental work, DFT calculations were used.
Section snippets
Synthesis SA-g-P(AAc-co-MA)/TiO2 hydrogel nanocomposite
According to the research design, in the presence of TiO2NPs, KMBA as a cross-linked agent, and PS as initiators, we synthesized the P(AAc-co-MA) grafted SA using a free radical graft co-polymerization approach [21]. Different concentrations of TiO2 (150 mg) NPs were placed in 20 ml of the distilled water in a reaction flask and shaken for 5 hours before being ultra-sonicated for 3 hours. Then, 0.5 g of SA was dissolved in the reaction mixture with constant stirring. The reaction mixture was
Characterization of the synthesized composite by FT-IR
Fig. 1 represents the infrared spectrum of SA-g-P(AAc-co-MA) hydro-gel and SA-g-P (AAc-co-MA)/TiO2 hydro-gel nanocomposite in 4000–400 cm−1. The SA-g-P(AAc-co-MA) spectrum showed two bands at 3430 and 2920 cm−1, which can be related to the stretching of –OH and CH2 groups, respectively. The bands at 1600 and 1420 cm−1 can be assigned to the -COO groups. Arabinosyl units are responsible for the 950 and 1100 cm−1, respectively. Moreover, broadband at 892 cm−1 confirms the glycosidic backbone. The
Effect of contacting time
The adsorption rate would be very significant when preparing batch adsorption experiments, according to the studies. Thus, the effect of the contact equilibrium over the adsorption of BG dye was studied [32]. BG dye adsorption increased significantly until the contact time reached 60 min at 25 °C. After that, increasing contact time showed no improvement in the adsorption; hence, the utmost contact equilibrium time has been chosen as 60 min for other experiments (Fig. 6).
Effect of initial concentration of dye
Adsorptive removal of
Adsorption kinetic modeling
The pseudo-first-order and pseudo-second-order models were used to analyze the rate of adsorption and probable absorption mechanisms of lead onto SA-g-P(AAc-co-MA)/TiO2 nanocomposite. The pseudo-first-order model is given as [44]:
Determination of adsorption isotherm parameters
Adsorption isotherm refers to the fraction of the sorbate molecules partitioned between solid and liquid phases at equilibrium. The dye absorption onto the SA-g-P(AAc-co-MA)/TiO2 nanocomposite was modeled using Langmuir and Freundlich adsorption models.
Conclusion
This study shows the low-cost SA-g-P(AAc-co-MA)/TiO2 nanocomposite as a candidate adsorbent to remove the dye. The batch tests indicated that the optimum adsorption of 100–1000 mg.L−1 of the dye from the industrial wastewater was at a pH = 6.6, t = 60 min, T = 25 °C, 260 rpm, and 0.05 g of the adsorbent mass. According to FESEM and TEM images, the adsorbent nature was changed after the dye adsorption, and a large amount of dye was accumulated over the surface of the adsorbent. Furthermore,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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