Instructive analysis of engineered carbon materials for potential application in water and wastewater treatment

Comprehensive insights into the application of graphene-based aerogels for metals removal from aqueous media: Surface chemistry, mechanisms, and key features

Efficient removal of heavy metals and other toxic metal pollutants from wastewater is essential to protect human health and the surrounding vulnerable ecosystems. Therefore, significant efforts have been invested in developing practical and sustainable tools to address this issue, including high-performance adsorbents. In this respect, within the last few years, graphene-based aerogels/xerogels/cryogels (GBAs) have emerged and drawn significant attention as excellent materials for removing and recovering harmful and valuable metals from different aqueous media. Such an upward trend is mainly due to the features of the aerogel materials combined with the properties of the graphene derivatives within the aerogel's network, including the GBAs' unique three-dimensional (3D) porous structure, high porosity, low density, large specific surface area, exceptional electron mobility, adjustable and rich surface chemistry, remarkable mechanical features, and tremendous stability. This review offers a comprehensive analysis of the fundamental and practical aspects and phenomena related to the application of GBAs for metals removal. Herein, we cover all types of (bottom-up) synthesized GBAs, including true microporous graphene-based aerogels as well as other 3D graphene-based open-cell interconnected mesoporous and macroporous aerogels, foams, and sponges. Indeed, we provide insights into the fundamental understanding of the GBAs' suitability for such an important application by revealing the mechanisms involved in metals removal and the factors inducing and controlling the highly selective behavior of these distinctive adsorbents. Besides conventional adsorptive pathways, we critically analyzed the ability of GBAs to electrochemically capture metal pollutants (i.e., electrosorption) as well as their efficiency in metals detoxification through reductive mechanisms (i.e., adsorption-reduction-readsorption). We also covered the reusability aspect of graphene aerogels (GAs)-based adsorbents, which is strongly linked to the GBAs' outstanding stability and efficient desorption of captured metals. Furthermore, in view of their numerous practical and environmental benefits, the development and application of magnetically recoverable GAs for metals removal is also highlighted. Moreover, we shed light on the potential practical and scalable implementation of GBAs by evaluating their performance in continuous metals removal processes while highlighting the GBAs' versatility demonstrated by their ability to remove multiple contaminants along with metal pollutants from wastewater media. Finally, this review provides readers with an accessible overview and critical discussion of major recent achievements regarding the development and applications of GAs-based adsorbents for metal ions removal. Along with our recommendations and suggestions for potential future work and new research directions and opportunities, this review aims to serve as a valuable resource for researchers in the field of wastewater treatment and inspire further progress towards developing next-generation high-performance GBAs and expanding their application.

Nitrogen-Doped Biochar for Enhanced Peroxymonosulfate Activation to Degrade Phenol through Both Free Radical and Direct Oxidation Based on Electron Transfer Pathways

Nowadays, super nitrogen-doped biochar (SNBC) material has become one of the most promising metal-free catalysts for activating peroxymonosulfate (PMS) to degrade organic pollutants. To understand the evolution of SNBC properties with fabrication conditions, a variety of SNBC materials were prepared and characterized by elemental analysis, N2 adsorption-desorption, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. We systematically investigated the activation potential of these SNBC materials for PMS to degrade phenol. SN1BC-800 with the best catalytic performance was obtained by changing the activation temperatures and the ratio of biochar to melamine. The effects of catalyst dosage, the PMS concentration, pH, and reaction temperature on phenol degradation were studied in detail. In the presence of 0.3 g/L SN1BC-800 and 1 g/L PMS, the removal rate of 20 mg/L phenol could reach 100% within 5 min. According to electron paramagnetic resonance spectra and free radical quenching experiments, a nonfree radical pathway of phenol degradation dominated by 1O2 and electron transfer was proposed. More interestingly, the excellent catalytic performance of the SN1BC-800/PMS system is universally applicable in the degradation of other typical organic pollutants. In addition, the degradation rate of phenol is still over 80% after five reuses, which shows that the SN1BC-800 catalyst has high stability and good application prospects in environmental remediation.

Photocatalytic degradation of parabens: A comprehensive meta-analysis investigating the environmental remediation potential of emerging pollutant

The increasing prevalence of paraben compounds in the environment has given rise to concerns regarding their detrimental impacts on both ecosystems and human health. Over the past few decades, photocatalytic reactions have drawn significant attention as a method to accelerate the otherwise slow degradation of these pollutants. The current study aims to evaluate the current efficacy of the photocatalytic method for degrading parabens in aqueous solutions. An extensive literature review and bibliometric analysis were conducted to identify key research trends and influential areas in the field of photocatalytic paraben degradation. Studies were screened based on the predetermined inclusion and exclusion criteria, which led to 13 studies that were identified as being appropriate for the meta-analysis using the random effects model. Furthermore, experimental parameters such as pH, paraben initial concentration, catalyst dosage, light intensity, and contact time have been reported to have key impacts on the performance of the photocatalytic degradation process. A comprehensive quantitative assessment of these parameters was carried out in this work. Overall, photocatalytic techniques could eliminate parabens with an average degradation efficiency of >80 %. The findings of the Egger's test and the Begg's test were statistically not significant suggesting potential publication bias was not observed. This review provides a holistic understanding of the photocatalytic degradation of parabens and is anticipated to encourage more widespread adoption of photocatalytic procedures as a suitable method for the elimination of parabens from aqueous solutions, opening new avenues for future research in this direction.

Linker-Functionalized Phosphinate Metal-Organic Frameworks: Adsorbents for the Removal of Emerging Pollutants

Metal-organic frameworks (MOFs) are attracting increasing attention as adsorbents of contaminants of emerging concern that are difficult to remove by conventional processes. This paper examines how functional groups covering the pore walls of phosphinate-based MOFs affect the adsorption of specific pharmaceutical pollutants (diclofenac, cephalexin, and sulfamethoxazole) and their hydrolytic stability. New structures, isoreticular to the phosphinate MOF ICR-7, are presented. The phenyl ring facing the pore wall of the presented MOFs is modified with dimethylamino groups (ICR-8) and ethyl carboxylate groups (ICR-14). These functionalized MOFs were obtained from two newly synthesized phosphinate linkers containing the respective functional groups. The presence of additional functional groups resulted in higher affinity toward the tested pollutants compared to ICR-7 or activated carbon. However, this modification also comes with a reduced adsorption capacity. Importantly, the introduction of the functional groups enhanced the hydrolytic stability of the MOFs.

Advances and prospects of carbon dots for microplastic analysis

Microplastics have become the world's most emerging pollutants today due to the ubiquitous use of plastics in everyday life and their ability to migrate from micro to nanoscale to every corner of the natural world, leading to ecological imbalances and global catastrophes. However, a standardized method for separating and analyzing microplastics from actual food or environmental samples has not been established. Therefore, it is necessary to develop a simple, fast, cost-effective, and accurate method that can accurately measure the degree of contamination of microplastics. As one of these methods, fluorometry has been proposed as a cost-effective method to detect, quantify and differentiate individual plastic particles. Therefore, this review discussed the technique for analyzing microplastics using fluorescent carbon dots (CDs). This review provided an overview of the impact of microplastics and the feasibility of using CDs to detect and analyze microplastics. In particular, this review will discuss novel microplastic analysis methods using CD and future application studies. The method using CDs will overcome the limitations of current microplastic analysis technology and may become a new method for detecting and analyzing microplastics.

The uses of transcriptomics and lipidomics indicated that direct contact with graphene oxide altered lipid homeostasis through ER stress in 3D human brain organoids

The potential uses of graphene-based nanomaterials (NMs) in various fields lead to the concern about their neurotoxicity, considering that graphene-based NMs are capable to cross blood brain barrier (BBB) and enter central nervous system (CNS). Although previous studies reported the possibility of graphene-based NM exposure to alter lipid homeostasis in animals or cultured neurons, recent studies suggested the need to use 3D human brain organoids for mechanism-based toxicological studies as this model might better recapitulate the complex human brains. Herein, we used multi-omics techniques to investigate the mechanisms of graphene oxide (GO) on lipid homeostasis in a novel 3D brain organoid model. We found that 50 μg/mL GO induced cytotoxicity but not superoxide. RNA-sequencing data showed that 50 μg/mL GO significantly up-regulated and down-regulated 80 and 121 genes, respectively. Furthermore, we found that GO exposure altered biological molecule metabolism pathways including lipid metabolism. Consistently, lipidomics data supported dose-dependent alteration of lipid profiles by GO in 3D brain organoids. Interestingly, co-exposure to GO and endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid (4-PBA) decreased most of the lipid classes compared with the exposure of GO only. We further verified that exposure to GO promoted ER stress marker GRP78 proteins, which in turn activated IRE1α/XBP-1 axis, and these changes were partially or completely inhibited by 4-PBA. These results proved that direct contact with GO disrupted lipid homeostasis through the activation of ER stress. As 3D brain organoids resemble human brains, these data might be better extrapolated to humans.

Role of emerging chitosan and zeolite-modified adsorbents in the removal of nitrate and phosphate from an aqueous medium: A comprehensive perspective

Due to industrialization and population growth, freshwater supplies are diminishing and becoming impure with high organic pollutant concentrations such as nitrate and phosphate, which shows a high adverse impact on aquatic and human lives. In drinking water sources, particularly groundwater, nitrate is considered as one of the major pollutants which causes methemoglobinemia (in newborn infants), carcinogenic activities and diabetes. Excess concentration of phosphate leads to eutrophication and death of aquatic species due to reduced dissolved oxygen content. Therefore, all countries must implement highly effective technologies for treating wastewater. Chitosan and zeolite are naturally occurring and cost-effective adsorbent materials with a higher surface area that exhibit greater nitrate and phosphate adsorption. Surface modification of chitosan and zeolite increases the adsorption capacity of adsorbents for the removal of both anions selectively. This paper reviews the current development of modified chitosan and zeolite adsorbents for anion adsorption, with an emphasis on modification by zero and multivalent metals and metal oxides, different surfactants, biomass-derived carbon, and natural and synthetic polymers. Multiple adsorption parameters, optimum adsorption condition, adsorption mechanism, regeneration study, research gap and future aspects have been explained for further research work.

Three-Dimensional Reduced Graphene Oxide Hybrid Nano-Silver Scaffolds with High Antibacterial Properties

In recent years, hazardous wastewater treatment has been a complex and global problem. In this work, by considering the antimicrobial activity of Ag nanoparticles (AgNPs) and reduced graphene oxide (rGO), we constructed an antibacterial device (G-AgNP) with AgNPs conformably deposited onto a 3D scaffold of reduced graphene oxide in situ. The major limitation, which is difficult to recycle, of two-dimensional graphene-silver composite materials in previous studies is improved. Characterization techniques, SEM, TEM, XRD, and XPS, confirmed the synthesis of nanocomposites. Attributed to its larger specific area, more active sites, and synergistic enhancement, the G-AgNP device demonstrated the best bacterial removal capacity, with an antibacterial rate for both E. coli and S. aureus as high as 100% at quite low AgNP contents. The reported G-AgNP has potential application as a wearable sewage treatment device and for the protection of wearable sensors as a promising sterilizing candidate based on its high and stable antibacterial efficiency.

Leveraging the potential of silver nanoparticles-based materials towards sustainable water treatment

Increasing demand of pure and accessible water and improper disposal of waste into the existing water resources are the major challenges for sustainable development. Nanoscale technology is an effective approach that is increasingly being applied to water remediation. Compared to conventional water treatment processes, silver nanotechnology has been demonstrated to have advantages due to its anti-microbial and oligodynamic (biocidal) properties. This review is focused on environmentally friendly green syntheses of silver nanoparticles (AgNPs) and their applications for the disinfection and microbial control of wastewater. A bibliometric keyword analysis is conducted to unveil important keywords and topics in the utilisation of AgNPs for water treatment applications. The effectiveness of AgNPs, as both free nanoparticles (NPs) or as supported NPs (nanocomposites), to deal with noxious pollutants like complex dyes, heavy metals as well as emerging pollutants of concern is also discussed. This knowledge dataset will be helpful for researchers to identify and utilise the distinctive features of AgNPs and will hopefully stimulate the development of novel solutions to improve wastewater treatment. This review will also help researchers to prepare effective water management strategies using nano silver-based systems manufactured using green chemistry.

Graphene oxide links alterations of anti-viral signaling pathways with lipid metabolism via suppressing TLR3 in vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs), the main cells constructing blood vessels, are important in the regulation of the pathophysiology of vascular systems; however, relatively few studies have investigated the influence of nanomaterials (NMs) on VSMCs. In this study, we found that the interaction between graphene oxide and human VSMCs led to the cytotoxicity and morphological changes of cells. Because transcriptomic data suggested that graphene oxide decreased anti-viral signaling pathways via decreasing Toll-like receptor 3 (TLR3), we further verified that graphene oxide decreased interferon induced protein with tetratricopeptide repeats 1 (IFIT1) and the radical S-adenosyl methionine domain containing 2 (RSAD2), and TLR3-downstream genes involved in anti-viral responses. Due to the involvement of RSAD2 in lipid dysfunction, we also verified that graphene oxide disrupted lipid homeostasis and increased adipose triglyceride lipase (ATGL). Adding TLR3 agonist polyinosinic:polycytidylic acid (Poly IC) partially increased TLR3-downstream protein interleukin-8 (IL-8) and some lipid classes, particularly lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE), in graphene oxide-exposed VSMCs. In mice receiving repeated intravenous injection of graphene oxide, significantly decreased TLR3, IFIT1 and RSAD2 but increased ATGL proteins were observed in aortas. We conclude that graphene oxide altered anti-viral signaling pathways and lipid metabolism via decreasing TLR3 in VSMCs.

A Composite Fabric with Dual Functions for High-Performance Water Purification

The dilemma of diminishing freshwater resources caused by water pollution has always impacted human life. Solar-driven interfacial evaporation technology has the potential for freshwater production via solar-driven distillation. However, in solar-driven interfacial evaporation technology, it is difficult to overcome the problem of wastewater containing various contaminants. In this work, we propose a bifunctional fabric created by depositing titanium dioxide@carbon black nanoparticles onto cotton fabric (TiO₂@CB/CF). The TiO₂@CB/CF has a coupling effect that includes the photothermal effect of CB and photocatalysis of TiO₂, and it can not only generate clean water but can also purify contaminated water. The resulting bifunctional fabric can achieve an outstanding water evaporation rate of 1.42 kg m^-2 h^-1 and a conversion efficiency of 90.4% in methylene blue (MB) solution under one-sun irradiation. Simultaneously, the TiO₂@CB/CF demonstrates a high photocatalytic degradation of 57% for MB solution after 2 h with light irradiation. It still shows a good photocatalysis effect, even when reused in an MB solution for eight cycles. Furthermore, the TiO₂@CB/CF delivers excellent performance for actual industrial textile dyeing wastewater. This bifunctional fabric has a good application prospect and will provide a novel way to resolve the issue of freshwater scarcity.

Nanomaterials for microplastic remediation from aquatic environment: Why nano matters?

The contamination of microplastics in aquatic environment is regarded as a serious threat to ecosystem especially to aquatic environment. Microplastic pollution associated problems including their bioaccumulation and ecological risks have become a major concern of the public and scientific community. The removal of microplastics from their discharge points is an effective way to mitigate the adverse effects of microplastic pollution, hence has been the central of the research in this realm. Presently, most of the commonly used water or wastewater treatment technologies are capable of removing microplastic to certain extent, although they are not intentionally installed for this reason. Nevertheless, recognizing the adverse effects posed by microplastic pollution, more efforts are still desired to enhance the current microplastic removal technologies. With their structural multifunctionalities and flexibility, nanomaterials have been increasingly used for water and wastewater treatment to improve the treatment efficiency. Particularly, the unique features of nanomaterials have been harnessed in synthesizing high performance adsorbent and photocatalyst for microplastic removal from aqueous environment. This review looks into the potentials of nanomaterials in offering constructive solutions to resolve the bottlenecks and enhance the efficiencies of the existing materials used for microplastic removal. The current efforts and research direction of which studies can dedicate to improve microplastic removal from water environment with the augmentation of nanomaterial-enabled strategies are discussed. The progresses made to date have witnessed the benefits of harnessing the structural and dimensional advantages of nanomaterials to enhance the efficiency of existing microplastic treatment processes to achieve a more sustainable microplastic cleanup.

Statistical evaluation of cow-dung derived activated biochar for phenol adsorption: Adsorption isotherms, kinetics, and thermodynamic studies

Sustainable and economical wastewater treatment forms a vital step towards long-term sustainability of petrochemical refineries and industries. An affordable solution to this challenge is to employ biowaste as the key consumable active component. This paper describes the synthesis and characterization of activated biochar derived from cow-dung, a readily available raw material in low-resource settings, and its application for adsorption of phenol, one of the major pollutants in industrial wastewater. Adsorption parameters are optimized by using response surface methodology. Phenol adsorption equilibrium and kinetics data are well fitted to Freundlich isotherm (R² = 0.97) and pseudo-second-order model (R² = 0.99), respectively. The maximal adsorption capacity (518.89 mg/g) was attained using the Langmuir isotherm model at pH 6.0. Negative values of thermodynamic parameters confirmed the spontaneity, feasibility, and exothermic behaviour of adsorption reaction. The results demonstrate that synthesized activated biochar showed an excellent phenol adsorption capacity of 98.8 %.

A Comprehensive Study on the Applications of Clays into Advanced Technologies, with a Particular Attention on Biomedicine and Environmental Remediation

In recent years, a great interest has arisen around the integration of naturally occurring clays into a plethora of advanced technological applications, quite far from the typical fabrication of traditional ceramics. This “second (technological) life” of clays into fields of emerging interest is mainly due to clays’ peculiar properties, in particular their ability to exchange (capture) ions, their layered structure, surface area and reactivity, and their biocompatibility. Since the maximization of clay performances/exploitations passes through the comprehension of the mechanisms involved, this review aims at providing a useful text that analyzes the main goals reached by clays in different fields coupled with the analysis of the structure-property correlations. After providing an introduction mainly focused on the economic analysis of clays global trading, clays are classified basing on their structural/chemical composition. The main relevant physicochemical properties are discussed (particular attention has been dedicated to the influence of interlayer composition on clay properties). Lastly, a deep analysis of the main relevant nonconventional applications of clays is presented. Several case studies describing the use of clays in biomedicine, environmental remediation, membrane technology, additive manufacturing, and sol-gel processes are presented, and results critically discussed.

Current perspective of innovative strategies for bioremediation of organic pollutants from wastewater

Organic contaminants in water are a growing environmental threat to sustainable development, with detrimental effects on the biosphere. In recent years, researchers have increasingly focused their attention on the area of bioremediation as an important tool to eliminate harmful pollutants from the environment. This review examines the application of bioremediation technologies to the removal of organic pollutants, with an emphasis on hydrocarbons and textile dyes. It applies a descriptive bibliometric analysis to study statistical practicality-vs-applicability of bioremediation of emerging organic pollutants. The paper identifies efficient pathways for bioremediation of different types of organic pollutants and outlines the potential for an eco-friendly and economical approach for the biological remediation of micropollutants by microalgae. Facts and figures on various hazardous pollutants, constraints in their current removal from water at an industrial level, and promising future solutions are carefully presented here.

The photocatalytic performance and mechanism of magnetically retrievable Z-scheme Cr2O3–Fe3O4/C hetero-nanostructure polyhedra

Magnetically retrievable Cr2O3–Fe3O4/C hetero-nanostructure polyhedra have been fabricated. The formation of Z-scheme Cr2O3–Fe3O4/C obviously improves the visible light absorption and promotes the separation of photogenerated charge carriers.