Fabrication of graphene oxide decorated with poly(dimethyl amino ethyl methacrylate) brush for efficient Cr(VI) adsorption from aqueous solution

Abstract

Confronting the severe health threats and environmental impacts of Cr(VI) in aquatic environments demands innovative and effective remediation approaches. In this study, Graphene oxide (GO)-decorated poly(dimethyl amino ethyl methacrylate) (PDMAEMA) brush nanocomposites (GOP1, GOP2, GOP3, and GOP4) were fabricated using atom transfer radical polymerization (ATRP) by the “graft from” method. The resulting nanocomposites were utilized for removing Cr(VI) with good adsorption performance due to the electrostatic interaction of protonated nitrogen groups in the brush chains with negatively charged particles in the solution. The kinetic model of pseudo-second-order best represented the contaminants' adsorption characteristics. The Weber–Morris model further indicated that surface adsorption and intraparticle diffusion mechanisms primarily controlled the adsorption procedure. Additionally, the Langmuir and Temkin isotherm models were found to most accurately represent the adsorption characteristics of the pollutants on the nanocomposites, and GOP4 can achieve the maximum adsorption capacity of 164.4 mg·g−1. The adsorbents' capacity maintains above 85% after five cycles of adsorption-desorption. The nanocomposites in this study demonstrate promising potential for eliminating Cr(VI) from aqueous solutions.

1. Introduction

Potable water quality has deteriorated in recent years due to rapid advancements in urbanization and industrialization, increasing population numbers, excessive utilization of natural water resources, and various anthropogenic influences exerted by human activities [1]. Heavy metals are one type of water-soluble pollutant adversely affecting human health, aquatic ecosystems, and the environment [2], and the primary heavy metal commonly present in wastewater is the chromium (Cr) ion [3] with two stable oxidation states, Cr(III) and Cr(VI); the latter is much more toxic [4]. Due to the presence of Cr ion in various industrial wastewater, such as the ceramics industry and steel fabrication, and its carcinogenic nature, which can lead to various health issues [5], the removal of Cr from wastewater is worth investigating. Based on the World Health Organization (WHO) announcement, the maximum allowable concentration of Cr(VI) for inland surface water and drinking water is 100 and 50 mg·L−1, respectively [3].

Various treatment techniques have been explored for removing Cr(VI) from wastewater with their disadvantages besides the benefits. For example, membrane filtration is expensive compared to other methods, but the efficiency is better than most. Another example is coagulation, which is affordable but requires many chemicals or the ion exchange method, which is easy to operate with high efficiency but has fouling and concentrate disposal issues [5,6]. Adsorption is one of the main techniques due to its convenience, flexibility in design and operation, cost-effectiveness, simplicity, and high efficiency [7]. Various types of adsorbents containing carbon [8], polymer [9], metallic [10], and mineral-based [11] composites have been used to remove pollutants. Graphene oxide (GO), a monolayer arrangement of carbon atoms with distinct physical and chemical properties, such as abundant oxygenous functional groups and large surface area, is a suitable precursor in designing the adsorbents made for Cr(VI) remediation. Various additives have been introduced to enhance the adsorption capabilities. Freire et al. [12] enhanced the relative adsorption of Cr(VI) in solutions containing multiple elements by modification of the magnetite and GO composite with amino groups (MAG-GO1-NH2). The adsorption capacity of 0.574 mmol·g−1 was obtained due to the −NH3+ groups' presence and easy binding with anionic Cr(VI) ions. In general, polymers with nitrogen-containing functional groups exhibit significant potential as contributors to selective Cr(VI) adsorption. This is attributed to the presence of lone pair electrons on nitrogen atoms, allowing them to accept protons and convert them into positively charged groups when exposed to an acidic environment. This enables electrostatic interaction with Cr(VI) anionic species. Notable GO-based adsorbents with nitrogen-containing groups have been reported, but further development is needed to enhance adsorption capacity and reusability.