Heavy Metals In Wastewater Research Articles

Preparation of Magnetic Activated Carbon by Activation and Modification of Char Derived from Co-Pyrolysis of Lignite and Biomass and Its Adsorption of Heavy-Metal-Containing Wastewater

Adsorption with activated carbon (AC) is an important method for the treatment of heavy metal wastewater, but there are still certain challenges in the separation and reuse of activated carbon. The preparation of magnetic activated carbon (MAC) by modifying AC is one of the effective means to realize the separation of AC from solution after the adsorption process. In this work, lignite and poplar leaves were used as raw materials for co-pyrolysis, and the co-pyrolysis char was activated and modified to prepare MAC. The structure and properties were characterized by VSM, N2 adsorption, SEM, XRD, and FT-IR. At the same time, the adsorption performance of MAC on wastewater containing Pb and Cd ions was studied. The results show that the prepared MAC contains Fe3O4, and the saturation magnetization (Ms) of the MAC is 13.83 emu/g; the specific surface area of the MAC is 805.86 m2/g, and the micropore volume is 0.23 cm3/g; the MAC exhibited a good porous structure. When the pH value of the solution was 5, the adsorption time was 120 min, the dosage of MAC was 4 g/L, the initial concentration of Pb ion solution was 50 mg/L, and that of Cd ion solution was 25 mg/L, and the adsorption temperature was 30 °C, the adsorption efficiency of Pb, Cd ions were 84.40 and 78.80%, respectively, and the adsorption capacities were 10.55 and 4.93 mg/g, respectively. The adsorption of Pb and Cd ions by MAC conforms to the Langmuir adsorption model, which is a monolayer adsorption. The adsorption process is mainly chemical adsorption, which can be better described by the pseudo-second-order model. The adsorption thermodynamic analysis showed that the adsorption of Pb and Cd ions by MAC was a spontaneous reaction, and the higher the temperature, the stronger the spontaneity.

Floating-separation adsorbent for methylene blue and Pb(II) removal: Structure construction and adsorption mechanism

Inferior solid–liquid separation behavior and inadequate adsorption capacity are the main bottlenecks of current wastewater treatment adsorbents, especially in the purification of wastewater containing dyes and heavy metals. Accordingly, a novel floating separation adsorbent with polymeric chain structure, hollow glass sphere-g-(3-aminopropyl) triethoxysilane-g-poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (APHGS-g-P(AMPS)), was fabricated through an electrophilic addition post-grafting strategy. The obtained APHGS-g-P(AMPS) exhibited satisfactory adsorption for methylene blue (MB) and lead ion (Pb(II)), as well as efficient flotation. Adsorption behavior analysis showed that the Pseudo-second-order kinetic model and Langmuir isotherm model were suitable for describing the adsorption process, and the maximum adsorption capacities for MB and Pb(II) were 249.33 and 345.93 mg·g−1 (313.15 K), respectively. Analysis of the adsorption mechanism indicated that the sulfonic acid group exhibited excellent universal adsorption for MB and Pb(II), which played a crucial role in the adsorption process. Furthermore, the efficient grafting of P(AMPS) polymerized chains onto the adsorbent was the pivotal factor to enhance adsorption. This study provided an efficient electrophilic addition post-grafting strategy for the structural design and functional modification of floating separation adsorbents. The results of this study are expected to have positive implications for the efficient purification of dyes and heavy metals wastewater.

Enhanced visible-light-driven photocatalytic activity of bi-phase titanium dioxide @ covalent organic framework Z-scheme system for photocatalytic removal of Cr (Ⅵ)

The discharge of industrial heavy metal wastewater not only leads to environmental pollution, but also harms human health, so it is imperative to control heavy metal pollution. In the current work, a sequence of anatase/brookite TiO2@COF with different mass ratios, bi-phase TiO2 and bare COF were successfully synthesized by simple hydrothermal synthesis. The photocatalytic activity of the prepared catalysts was assessed by reducing Cr(Ⅵ) in model pollutant (K2Cr2O7). Under the condition of pH = 3, the Cr(Ⅵ) reduction rate of TiO2@COF-4 was as high as 99.19% in 30 min. The photocatalytic activity of TiO2@COF-4 remained stable in four consecutive cycles, suggesting that it has a potential application prospect for the removal of Cr(Ⅵ) in the actual environment. The morphology and structure of photocatalysts were observed by different techniques (SEM/EDS, HRTEM, BET analysis, XRD, FTIR and XPS). The specific reasons for the enhancement of photocatalytic performance of materials were explored by different methods (PL, UV–vis DRS, Mott-Schottky plots, I-T curves and EIS). Finally, we concluded that the photocatalytic system of TiO2@COF-4 may follow the typical direct Z- scheme mechanism. This work provides an effective solution for the water treatment of heavy metal pollution.

Concentrations of Zn, Mn and Al in wood chips from wood-based manufacturing industries

The elemental composition of wood chip samples manufactured in the wood industries at Batu Pahat were analyzed for their heavy metals composition. This study was aimed to prove that heavy metals can accumulate in wood and trees themselves without adding any wood treatment additives. ICP-MS analysis was conducted on the wastewater at the same manufacturing industry to evince the occurrence of the leaching process that causes the presence of heavy metals in the wastewater. The results of the experiments showed that Mn, Zn and Al were among the highest metal traces found in the wood chips. As a result, Mn concentrations in three different samples of wood chips were 83.6 mg/L, 88.1 mg/L, and 80.9 mg/L, whereas Zn amounts were 38.8 mg/L, 40.2 mg/L, and 37.7 mg/L. Furthermore, the amounts of Al traces in the three samples were 28.2 mg/L, 29.6 mg/L, and 30.7 mg/L, respectively. The study also found that the highest metal trace in wastewater shows a proportional value to the highest concentration of heavy metals in wood chips. Therefore, it can be concluded that, even though the whole chipping production process is considered to be a dry process, the wastewater generated after cleaning surfaces, storage tanks and machinery, causes heavy metal leaching and contributes to the presence of heavy metals in wastewater.

Heavy metal toxicity of drinking water: A silent killer

Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. Heavy metals are generally referred to as those metals which possess a specific density of more than 5 g/cm3 and adversely affect the environment and living organisms. These metals are essential to maintain various biochemical and physiological functions in living organisms when in very low concentrations, however they become noxious when they exceed certain threshold concentrations. The most commonly found heavy metals in waste water include arsenic, cadmium, chromium, and copper, lead, nickel, and zinc, all of which cause risks for human health and the environment. Heavy metals enter the surroundings by natural means and through human activities. Various sources of heavy metals include soil erosion, natural weathering of the earth's crust, mining, industrial effluents, urban runoff, sewage discharge, insect or disease control agents applied to crops etc. Some heavy metals, i.e. arsenic, lead, mercury, cadmium, chromium, aluminium causes drastic harmful effect on the environment and living organisms, mainly human beings.

Efficient simultaneous removal of tetracycline hydrochloride and Cr(VI) through photothermal-assisted photocatalytic-Fenton-like processes with CuOx/γ-Al2O3

Advanced oxidation processes (AOPs) based on photo-Fenton reaction has been widely used in refractory organic wastewater treatment. However, the mineralization rate and H2O2 utilization in AOPs is relatively low. Herein, a photothermal-assisted photocatalytic-Fenton-like process with CuOx/γ-Al2O3 catalyst was designed to solve the above issues. The utilization rate of H2O2 and mineralization rate of tetracycline hydrochloride (TC) in the 3%-CuOx/γ-Al2O3/H2O2/full spectrum light system were significantly increased to 72.0% and 74.3%, respectively, which were ascribed to the synergy of photothermal effect and photocatalytic-Fenton-like reaction. During the simultaneous removal of TC and Cr(VI), the reaction efficiency of 3%-CuOx/γ-Al2O3/H2O2/light system was much higher than that of 3%-CuOx/γ-Al2O3/H2O2 system. In addition, the 3%-CuOx/γ-Al2O3/H2O2/light system was not only active in wider pH range (3–9), but also effective in various organic pollutants and Cr(VI) coexisted solutions as well as different water conditions. More importantly, a possible photothermal-assisted photocatalytic-Fenton-like reaction mechanism for the simultaneous removal of TC and Cr(VI) in the CuOx/γ-Al2O3/H2O2/light system was proposed. This work may pave a new way for efficient simultaneous removal of refractory organic pollutants and heavy metals in wastewater.

Compressible amino-modified carboxymethyl chitosan aerogel for efficient Cu(II) adsorption from wastewater

Copper ions (Cu(II)) in water pose a huge threat to human health and ecosystem security. Therefore, developing eco-friendly and sustainable strategies to eliminate the toxicity risk of Cu(II) in the aqueous environment remains a great challenge. In this work, an elastic polyethyleneimine-modified carboxymethyl chitosan aerogel was developed via a freeze-drying process for the adsorption of Cu(II). The adsorption kinetic and isotherm experiments demonstrated that the adsorption process was monolayer chemisorption and the maximum adsorption capacity calculated from Langmuir model was 175.56 mg g−1. The obtained aerogels exhibited preferential selectivity for Cu(II) even when the competing cations and organics existed. Besides, about 0.93 g of aerogel realized continuous fixed-bed column filtration of industrial wastewater with an effective purification volume of 4.14 L. Mechanistic analysis via FTIR and XPS revealed that the excellent adsorption performance for Cu(II) might be attributed to the strong electrostatic force, Vander Waals' force and coordination of N/O -containing functional groups. It is worth mentioning that the adsorbed Cu(II) ions in the aerogel were converted into a reusable photocatalyst, avoiding the secondary leakage of heavy metals. This work opened a door to synthesize carboxymethyl chitosan aerogel, promising for heavy metal wastewater treatment and realizing the concept of waste utilization.

Adsorptive Removal of Multi-Metal Ions in Wastewater Using Electrospun Cellulose Acetate / Iron-Modified Nanozeolite Nanofibrous Membrane

In this undertaking, nanofibrous membrane of cellulose acetate (CA) with varying concentrations of iron-modified nanozeolite (Fe-MNZ) were produced through electrospinning technique for the simultaneous adsorption of Ni2+, Co2+ and Cu2+ heavy metal ions in wastewater. The electrospun nanofibrous membranes (ENMs) produced underwent different characterization techniques to determine the effect of Fe-MNZ addition on the ENM of CA in terms of porosity and adsorption capacity. Porometry results and contact angle measurements confirmed the increase in fiber diameter through the decrease in pore size and increase in the wettability of the ENMs produced. The adsorption experiment showed that ENM blend 2, M2, containing 1.0 wt.% Fe-MNZ had the highest removal efficiency for Ni2+ ions at around 79.20%, while ENM blend 3, M3, which contained 1.2 wt.% Fe-MNZ had adsorbed most of the Co2+ and Cu2+ ions with removal efficiencies equal to 54.04% and 100%, respectively. Adsorption of Ni2+ and Co2+ ions was governed by Freundlich isotherm and pseudo-first order kinetics, whereas the adsorption data of Cu2+ ions best fitted both Langmuir and Freundlich isotherms, and pseudo-second order kinetics. Lastly, the adsorption of the heavy metal ions was verified by the results of SEM-EDX.

Hydrogel-Based Adsorbent Material for the Effective Removal of Heavy Metals from Wastewater: A Comprehensive Review.

Water is a vital resource that is required for social and economic development. A rapid increase in industrialization and numerous anthropogenic activities have resulted in severe water contamination. In particular, the contamination caused by heavy metal discharge has a negative impact on human health and the aquatic environment due to the non-biodegradability, toxicity, and carcinogenic effects of heavy metals. Thus, there is an immediate need to recycle wastewater before releasing heavy metals into water bodies. Hydrogels, as potent adsorbent materials, are a good contenders for treating toxic heavy metals in wastewater. Hydrogels are a soft matter formed via the cross-linking of natural or synthetic polymers to develop a three-dimensional mesh structure. The inherent properties of hydrogels, such as biodegradability, swell-ability, and functionalization, have made them superior applications for heavy metal removal. In this review, we have emphasized the recent development in the synthesis of hydrogel-based adsorbent materials. The review starts with a discussion on the methods used for recycling wastewater. The discussion then shifts to properties, classification based on various criteria, and surface functionality. In addition, the synthesis and adsorption mechanisms are explained in detail with the understanding of the regeneration, recovery, and reuse of hydrogel-based adsorbent materials. Therefore, the cost-effective, facile, easy to modify and biodegradable hydrogel may provide a long-term solution for heavy metal removal.

Insight into different removal behaviors and mechanism of heavy metals via sulfate-loaded layered double oxide

Sulfur-containing materials with high affinity toward heavy metals have recently aroused great research enthusiasm. Yet the removal differences and mechanisms for various heavy metals remain unclear in view of rarely systematical reports. In this regard, a sulfate-loaded adsorbent (MgAl-LDO@S) synthesized by precursor-calcination strategy was employed for investigating the removal differences of heavy metals (i.e., Pb(Ⅱ), Cd(Ⅱ) and Ni(Ⅱ), typical heavy metals in wastewater). As predicted, a diverse adsorption capability for metals on MgAl-LDO@S was observed, following the order of Pb(Ⅱ) (631.90 mg g−1) > Cd(Ⅱ) (208.27 mg g−1) > Ni(Ⅱ) (119.02 mg g−1). Both adsorption isotherm and kinetic demonstrated that the monolayer, heterogeneous-homogeneous, and multilayer adsorption occurred in Pb(Ⅱ), Cd(Ⅱ) and Ni(Ⅱ), respectively, which were controlled by chemisorption. Furthermore, the removal differences were deeply exploded via the combination of XRD, FT-IR and XPS analyses and contribution calculation. The ion exchange was the main adsorption mechanisms for Pb (II) with 44.77%, while complexation dominated in Cd(II) and Ni(II) removal, with the proportion of 53.36% and 55.89%, respectively. Besides, the solubility constant (Ksp) of precipitate, affinity of sulfate group, as well as the self-characteristic properties contributed to various removal ability for heavy metal ions (e.g., ionic radius, electronegativity, and hard-soft-acid-base attribute) as well.

Effect of pH on oxygen-induced abio-oxidation and removal of As from As-rich acid mine drainage in the co-existence of Zn(II)

Zn(II) enhances the adsorption of arsenate in heavy metal wastewater onto iron oxides, but the effect of Zn(II) on the removal of As during the oxidation of As(III) to As(V), corresponding to remediation of As-rich acid mine drainage (AMD) via oxidation-precipitation method, is still unclear. The rapid and efficient removal of As from As-rich AMD in the co-existence of Zn(II) was conducted through oxygen-induced abio-oxidation of Fe(II) and As(III) at slightly acidic to alkaline pH in this work. After 8-h reactions, arsenic removal and arsenite oxidation efficiencies reached 91.9–99.9% and 34.6–63.8%, which showed an evident rise at first and then decreased as the pH increased from 3 to 9. Maximum As removal and oxidation with the As-leaching stable solid product was observed at pH 5. Reactive oxygen species (ROS) contents involving Fenton-like reaction degree and solid product species were controlled by pH for As(III), As(V), Fe(II), Fe(III) and Zn(II) liquid-solid distribution as the probable mechanism. Almost all of arsenic and zinc were mainly immobilized by the produced Zn(II)–As(III + V)-bearing SO4-ferrihydrite at pH 5 with the higher short-term stability of the final solid due to higher As(V) in solid-phase and a small amount of zinc hydrogen arsenate produced. At higher pH, adsorbed-Zn(II) competition with ROS for solid surface sites negatively affected the Fenton-like reaction process for unstable Zn(II)–As(III + V)-bearing magnetite, causing the decrease of As removal and oxidation.

Janus Co@C/NCNT photothermal membrane with multiple optical absorption for highly efficient solar water evaporation and wastewater purification

Solar-driven interfacial water evaporation has emerged as a promising approach for green and sustainable production of clean water to alleviate freshwater shortage, especially in remote and arid regions. However, limited photothermal conversion efficiency and poor water transport remain challenges to achieve highly efficient solar water evaporation. In this study, we propose a facile strategy to construct a novel Janus photothermal membrane by combining highly hydrophobic nitrogen-doped carbon nanotubes encapsulating cobalt nanoparticles (Co@C/NCNT) with a hydrophilic nylon membrane, which enables simultaneous realization of asymmetric surface wettability and multiple optical absorption pathways. The as-fabricated Janus Co@C/NCNT evaporator achieves a high solar water evaporation rate of 1.55 kg m−2 h−1 and an evaporation efficiency of 89.7% under one sun irradiation, which are well maintained after 10 cycles. Meanwhile, the Janus evaporator can be used for practical purification of various simulated wastewater, such as dyeing sewage and heavy metal wastewater, with high rejection efficiency and long-term stability. This Janus evaporator design provides an efficient, low-cost solar water evaporation system for potential water purification.

Activated Carbon/Carborundum@Microcrystalline Cellulose core shell nano-composite: Synthesis, characterization and application for heavy metals adsorption from aqueous solutions

The ubiquitous existence of heavy metals in wastewater and natural water bodies has deteriorated the quality of water environment and exerted significant hazardous impacts on ecosystems. Herein, a novel effective Activated Carbon/Carborundum@Microcrystalline Cellulose core shell nano-composite (AC/CB/MCC) was synthesized to be utilized for aqueous solutions detoxification from As (III) and Cu (II) ions. Various principal characterizations including XRD, FTIR, SEM, TEM, BET surface area, and zeta potential were performed to examine the different characteristics of activated carbon, carborundum, microcrystalline cellulose and the synthesized AC/CB/MCC nano-composite. The kinetic studies illustrated that the pseudo-second-order is the most favorable model for ion adsorption among the examined models. The sorption experimental data of the optimized AC/CB/MCC were best fitted with the Freundlich isotherm with optimal adsorption capacities of 422.9 and 423.55 mg/g for As (III) and Cu (II) ions, respectively. The electrostatic interaction was the main mechanism for ion adsorption onto AC/CB/MCC nano-composite at moderate pH values (pH above 6), while the chemical complexation was the main mechanism at high acidic conditions (pH=2–6). This study would extend the potential application of Activated Carbon/Carborundum@Microcrystalline Cellulose nano-composite, acting as an exceptional active adsorbent for As (III) and Cu (II) ion adsorption in water treatment.

Enhanced adsorption of aqueous Pb(II) and Cu(II) by biochar loaded with layered double hydroxide: Crucial role of mineral precipitation

To improve heavy metal adsorption efficiency and investigate interaction mechanisms by biochar-based materials, MgAl-layered double hydroxide (MgAl-LDH) was loaded on the coconut shell biochar (BC) obtaining the composite (BC-LDH) for adsorptive decontamination of Pb(II) and Cu(II) in water. The removal capacities of BC-LDH (294 and 38.6 mg/g) was higher than BC (13.3 and 11.4 mg/g) and LDH (126 and 22.7 mg/g) for aqueous Pb(II) and Cu(II). The interaction mechanisms between BC-LDH and heavy metals were classified as mineral precipitation, cation exchange and isomorphic replacement, electrostatic attraction, and surface complexation according to the characterization results, and the corresponding adsorption capacity were named as Qpre, Qexc, Qele, and Qcom. The quantitative analysis indicated that the contributions of the above mechanisms of BC-LDH for Pb(II) and Cu(II) followed the order of Qpre > Qele > Qexc and Qpre > Qexc > Qele, respectively. The Qpre values reached 76.26% and 45.0%, suggesting the mineral precipitation was the dominant mechanism. The cation exchange and isomorphic replacement (44.18% for Cu(II)), as well as the electrostatic attraction (12.46% for Pb(II)), were also key contributions to the interaction mechanisms. Compared with BC, the Qpre increased and Qele decreased significantly, certified the combination of BC and LDH provided a kind of viable composite in heavy metal wastewater treatment.

The Application of Modified SBA-15 as a Chemosensor

: The Santa Barbara Amorphous (SBA-15), with a large surface area covered with abundant Si-OH active groups on the walls of its pores, can be modified with various organic compounds to build organic-inorganic hybrid materials, which can be used as a catalyst in organic reactions, drug delivery systems, nano sorbent due to its high capacity for removing heavy metals in waste water and as chemosensors for ions. Tunable and straight channels of SBA-15 facilitate the entrance and diffusion of ions through the channels. This paper presents a review of the past five years of literature covering the application of SBA-15 as an ions chemosensor in the liquid and gaseous media.

A novel metal-organic framework-derived ZnO@ZIF-8 adsorbent with high efficiency for Pb (II) from solution: Performance and mechanisms

A metal-organic framework (ZnO@ZIF-8) with great adsorption potential was developed using ZnO nanoparticles as a surface-active center and applied to lead removal from wastewater. The adsorption experiments were carried out and the related adsorption behaviors were investigated. The adsorbent shows excellent adsorption performance between pH 3–5. The maximum adsorption capacity of ZnO@ZIF-8 for Pb (II) was 689.36 mg/g at 303 K. The adsorptive process of Pb (II) onto ZnO@ZIF-8 conforms to the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamics illustrate that the adsorption process is chemical adsorption on a uniform surface. Selectivity experiments showed that ZnO@ZIF-8 had the strongest affinity with Pb (II). The adsorption-desorption cycle confirmed that ZnO@ZIF-8 was a reliable and recyclable adsorbent. XPS, Zeta potential and FT-IR analysis illustrate that the adsorption of Pb (II) by ZnO@ZIF-8 was concentrated in electrostatic adsorption and chelation. DFT calculation indicated that there are different types of Pb (II) combination mode (Pb-N and Pb-O) and the adsorption mainly depended on the chelation. This study presented herein played important roles in the governance of heavy metal waste-water pollution as a result of ZnO@ZIF-8 can effective selectivity cleanup of Pb (II).

Separation of Chitin from Shrimp and Application in Heavy Metal Wastewater Treatment

In this research work natural bio polymer “chitosan” was extracted using locally available shrimp shells and absorption of copper by chitosan was studied. Synthesis of chitosan involved four main stages as preconditioning, demineralization, deproteinization and deacetylation. Chitosan was characterized using Fourier Transform Infrared Spectroscopy (FTIR). The affinity of chitosan for cupper was studied using anhydrous CuCl2 solution as the heavy metal solution containing Cu (II) ions

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Fruit Peels as a Sustainable Waste for the Biosorption of Heavy Metals in Wastewater: A Review.

One of the environmental challenges that is currently negatively affecting the ecosystem is the continuous discharge of untreated industrial waste into both water sources and soils. For this reason, one of the objectives of this qualitative study of exploratory-descriptive scope was the review of scientific articles in different databases—Scopus, Web of Science, and Science Direct—published from 2010 to 2021 on the use of fruit peels as a sustainable waste in the removal of heavy metals present in industrial wastewater. For the selection of articles, the authors used the PRISMA guide as a basis, with which 210 publications were found and 93 were compiled. Considering the reported work, a content analysis was carried out using NVivo 12 Plus and VOSviewer 1.6.17 software. The results show that the fruits mentioned in these publications are lemon, banana, mango, tree tomato, pineapple, passion fruit, orange, coconut, avocado, apple, lulo, and tangerine. However, no studies were found with lulo and tree tomato peels. On the other hand, the heavy metals removed with the selected fruit peels were Pb+2, Cr+3, Cr+6, Ni+2, Cd+2, As+5, Cu+2, and Zn+2.

Surface Functionalization of Graphene Oxide with Hyperbranched Polyamide-Amine and Microcrystalline Cellulose for Efficient Adsorption of Heavy Metal Ions.

Graphene oxide (GO)-based adsorbents have received attention in the removal of heavy metal ions in wastewater due to its large specific surface area and oxygen-containing functional groups, which can enhance the interaction between GO and heavy metal ions. Many researchers are seeking economical and effective strategies to further improve the adsorption capacity of GO. In this study, hyperbranched polymers and cellulose were used to surface functionalize GO for the efficient adsorption of heavy metal ions. First, hyperbranched polyamide-amine (HPAMAM) functionalized GO was fabricated by the formation of an amide bond between the carboxyl group of GO and the amino group of HPAMAM, increasing the active groups on the GO surface and enhancing the affinity with heavy metal ions. Then, dialdehyde cellulose (DAC) obtained through the oxidation of microcrystalline cellulose was grafted onto GO/HPAMAM by forming a Schiff-based structure between the amino group of HPAMAM and aldehyde group of DAC. Interestingly, DAC formed micro/nano bumps on GO, which was beneficial to increase the hydroxyl number and contact area with heavy metal ions. The Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) results confirmed the successful synthesis of GO/HPAMAM/DAC. The obtained GO/HPAMAM/DAC adsorbent exhibited strong adsorption capacity and good cycle stability for heavy metal ions. The maximum adsorption capacities of Pb(II), Cd(II), and Cu(II) were 680.3, 418.4, and 280.1 mg/g at 298 K, which were better than those of most adsorbents reported. A pseudo-second-order kinetic model could well-describe the Pb(II), Cd(II), and Cu(II) adsorption onto GO/HPAMAM/DAC, and the equilibrium data fitted well with the Langmuir isotherm model. The adsorption of Pb(II), Cd(II), and Cu(II) was mainly attributed to the chelation or complexation of nitrogen- and oxygen-containing groups on the GO/HAPAMAM/DAC adsorbent. This study may provide a novel strategy for improving the adsorption performance of GO with hyperbranched polymers and cellulose.