Advances in Graphene-Based Magnetic and Graphene-Based/TiO2 Nanoparticles in the Removal of Heavy Metals and Organic Pollutants from Industrial Wastewater

New insights into the environmental application of hybrid nanoparticles in metal contaminated agroecosystem: A review

Heavy metals (HMs) contamination in agricultural soils is a major constraint to provide safe food to society. Cultivation of food crops on these soils, channels the HMs into the food chain and causes serious human health and socioeconomic problems. Multiple conventional and non-conventional remedial options are already in practice with variable success rates, but nanotechnology has proved its success due to higher efficiency. It also led the hypothesis to use hybrid nanoparticles (HNPs) with extended benefits to remediate the HMs and supplement nutrients to enhance the crop yield in the contaminated environments. Hybrid nanoparticles are defined as exclusive chemical conjugates of inorganic and/or organic nanomaterials that are combinations of two or more organic components, two or more inorganic components, or at least one of both types of components. HNPs of different elements like essential nutrients, beneficial nutrients and carbon-based nanoparticles are used for the remediation of metals contaminated soil and the production of metal free crops. Characterizing features of HNPs including particle size, surface area, reactivity, and solubility affect the efficacy of these HNPs in the contaminated environment. Hybrid nanoparticles have great potential to remove the HMs ions from soil solution and restrict their ingress into the root tissues. Furthermore, HNPs of essential nutrients not only compete with heavy metal uptake by plants but also fulfill the need of nutrients. This review provides a comprehensive overview of the challenges associated with application of HNPs in contaminated soils, environmental implications, their remediation ability, and factors affecting their dynamics in environmental matrices.

The photocatalytic process in the treatment of polluted water

Wastewaters often contain toxic organic pollutants with a possible adverse effect on human health and aquatic life upon exposure. Persistent organic pollutants such as dyes and pesticides, pharmaceuticals, and other chemicals are gaining extensive attention. Water treatment utilizing photocatalysis has recently received a lot of interest. Photocatalysis is cutting-edge, alternative technology. It has various advantages, including functioning at normal temperatures and atmospheric pressure, cheap prices, no secondary waste creation, and being readily available and easily accessible. This review presented a comprehensive overview of the advances in the application of the photocatalytic process in the treatment of highly polluted industrial wastewater. The analysis of various literature revealed that TiO₂-based photocatalysts are highly effective in degrading organic pollutants from wastewater compared to other forms of wastewater treatment technologies. The electrical structure of a semiconductor plays a vital role in the photocatalyst's mechanism. The morphology of a photocatalyst is determined by the synthesis method, chemical content, and technical characteristics. The scaled-up of the photoreactors will significantly help in curbing the effect of organic pollutants in wastewater.

Adsorption of Magenta Dye on PbO Doped MgZnO: Interpretation of Statistical Physics Parameters Using Double-Layer Models

This article reports the synthesis of PbO doped MgZnO (PbO@MgZnO) by a co-precipitation method, followed by an ultrasonication process. PbO@MgZnO demonstrates a significant adsorption capability toward Magenta Dye (MD). The greatest adsorption capability was optimized by varying parameters such as pH, MD concentration, and adsorbent dose. The kinetics study illustrates that the adsorption of MD on PbO@MgZnO follows the pseudo-second-order. The isotherm study revealed that Langmuir is best fitted for the adsorption, but with little difference in the R² value of Langmuir and Freundlich, the adsorption process cloud be single or multi-layer. The maximum adsorption capacity was found to be 333.33 mg/g. The negative ΔG refers to the spontaneity of MD adsorption on PbO@MgZnO. The steric parameters from statistical physics models also favor the multi-layer adsorption mechanism. As a function of solution temperature, the parameter n pattern has values of n = 0.395, 0.290, and 0.280 for 298, 308, and 318 K, respectively (i.e., all values were below 1). Therefore, horizontal molecule positioning and multiple locking mechanisms were implicated during interactions between MD and PbO@MgZnO active sites.

Highly efficient surface sequestration of Pb2+ and Cr3+ from water using a Mn3O4 anchored reduced graphene oxide: Selective removal of Pb2+ from real water

Owing to the ubiquitous existence of detrimental heavy metals in the environment, simple adsorption-oriented approaches are becoming increasingly appealing for the effective removal of Pb²⁺ and Cr³⁺ from water bodies. These techniques use nanocomposites (NC) of reduced graphene oxide (rGO) and Mn₃O₄ (rGO-Mn₃O₄), they employ a hydrothermal technique featuring NaBH₄ and NaOH solutions. Here, spectroscopic and microscopic instrumental techniques were used to evaluate the morphological and physicochemical characteristics of prepared reduced graphene oxide manganese oxide (rGO-Mn₃O₄), revealing that it possessed a well-defined porous structure with a specific surface area of 126 m² g^-1. The prepared rGO-Mn₃O₄ had significant adsorption efficiencies for Pb²⁺ and Cr³⁺, achieving maximum sequestration capacities of 130.28 and 138.51 mg g^-1 for Pb²⁺ and Cr³⁺, respectively, according to the Langmuir model. These adsorption capacities are comparable to or greater than those of previously reported graphene-based materials. The Langmuir isotherm and pseudo-second-order models adequately represented the experimental results. Thermodynamic analysis revealed that adsorption occurred through spontaneous endothermic reactions. Recycling studies showed that the developed r-GO-Mn₃O₄ had excellent recyclability, with <70% removal at the 5th cycle; its feasibility was evaluated using industrial wastewater, suggesting that Pb²⁺ was selectively removed from Pb²⁺ and Cr³⁺ contaminated water. The instrumental analysis and surface phenomena studies presented here revealed that the adsorptive removal processes of both heavy metals involved π electron donor-acceptor interactions, ion exchange, and electrostatic interactions, along with surface complexation. Overall, the developed rGO-Mn₃O₄ has the potential to be a high-value adsorbent for removing heavy metals.

A review on magnetic sensors for monitoring of hazardous pollutants in water resources

Water resources have long been of interest to humans and have become a serious issue in all aspects of human life. The disposal of hazardous pollutants in water resources is one of the biggest global concerns and poses many risks to human health and aquatic life. Therefore, the control of hazardous pollutants in water resources plays an important role, when it comes to evaluating water quality. Due to low toxicity, good electrical conductivity, facile functionalization, and easy preparation, magnetic materials have become a good alternative in recent years to control hazardous pollutants in water resources. In the present study, the idea of using magnetic sensors in controlling and monitoring of pharmaceuticals, pesticides, heavy metals, and organic pollutants have been reviewed. The water pollutants in drinking water, groundwater, surface water, and seawater have been discussed. The toxicology of water hazardous pollutants has also been reviewed. Then, the magnetic materials were discussed as sensors for controlling and monitoring pollutants. Finally, future remarks and perspectives on magnetic nanosensors for controlling hazardous pollutants in water resources and environmental applications were explained.

Removal of Heavy Metals from Wastewater Using Novel Polydopamine-Modified CNTs-Based Composite Membranes

The presence of major heavy metals including Pb2+, Cu2+, Co2+, Ni2+, Hg2+, Cr6+, Cd2+, and Zn2+ in water is of great concern because they cannot degrade or be destroyed. They are toxic even at very low concentrations. Therefore, it is necessary to remove such toxicants from water. In the current study, polydopamine carbon nanotubes (PD-CNTs) and polysulfone (PS) composite membranes were prepared. The structural and morphological features of the prepared PDCN composite membranes were studied using FTIR, XRD, SEM, and EDS. The potential application of PDCNs for heavy metal removal was studied for the removal of Pb2+, Cr6+, and Cd2+ from wastewater. The maximum removal efficiency of 96.1% was obtained for Cr6+ at 2.6 pH using a composite membrane containing 1.0% PD-CNTs. The removal efficiencies decreased by 64.1 and 73.4, respectively, by enhancing the pressure from 0.50 up to 0.85 MPa. Under the same circumstances, the percentages of Pb+2 removal at 0.49 bar by the PDCNS membranes containing 0.5% and 1.0% PD-CNT were 70 and 90.3, respectively, and decreased to 54.3 and 57.0, respectively, upon increasing the pressure to 0.85 MPa. The results showed that PDCNS membranes have immense potential for the removal of heavy metals from water.

Organic Dyes versus Adsorption Processing

Even in the first quarter of the XXI century, the presence of organic dyes in wastewaters was a normal occurrence in a series of countries. As these compounds are toxic, their removal from these waters is a necessity. Among the separation technologies, adsorption processing appeared as one of the most widely used to reach this goal. The present work reviewed the most recent approaches (first half of the 2021 year) regarding the use of a variety of adsorbents in the removal of a variety of organic dyes of different natures.

Graphene-Based Composites as Catalysts for the Degradation of Pharmaceuticals

The incessant release of pharmaceuticals into the aquatic environment continues to be a subject of increasing concern. This is because of the growing demand for potable water sources and the potential health hazards which these pollutants pose to aquatic animals and humans. The inability of conventional water treatment systems to remove these compounds creates the need for new treatment systems in order to deal with these class of compounds. This review focuses on advanced oxidation processes that employ graphene-based composites as catalysts for the degradation of pharmaceuticals. These composites have been identified to possess enhanced catalytic activity due to increased surface area and reduced charge carrier recombination. The techniques employed in synthesizing these composites have been explored and five different advanced oxidation processes-direct degradation process, chemical oxidation process, photocatalysis, electrocatalyis processes and sonocatalytic/sono-photocatalytic processes-have been studied in terms of their enhanced catalytic activity. Finally, a comparative analysis of the processes that employ graphene-based composites was done in terms of process efficiency, reaction rate, mineralization efficiency and time required to achieve 90% degradation.