The production of biochar from biomass and industrial wastes provides both environmental and economic sustainability. An effective way to ensure the sustainability of biochar is to produce high value-added activated carbon. The desirable characteristic of activated carbon is its high surface area for efficient adsorption of contaminants. Feedstocks can include a number of locally available materials with little or negative value, such as orchard slash and crop residue. In this context, it is necessary to determine and know the conversion effects of the feedstocks to be used in the production of activated carbon. In the study conducted for this purpose; several samples (piñon wood, pecan wood, hardwood, dried grass, Wyoming coal dust, Illinois coal dust, Missouri coal dust, and tire residue) of biomass and industrial waste products were investigated for their conversion into activated carbon. Small samples (approximately 0.02 g) of the feedstocks were pyrolyzed under inert or mildly oxidizing conditions in a thermal analyzer to determine their mass loss as a function of temperature and atmosphere. Once suitable conditions were established, larger quantities (up to 0.6 g) were pyrolyzed in a tube furnace and harvested for characterization of their surface area and porosity via gas sorption analysis. Among the samples used, piñon wood gave the best results, and pyrolysis temperatures between 600 and 650 °C gave the highest yield. Slow pyrolysis or hydrothermal carbonization have come to the fore as recommended production methods for the conversion of biochar, which can be produced from biomass and industrial wastes, into activated carbon.

It is a "kill two birds with one stone" method to convert invasive plants into hydrochar via hydrothermal carbonization as well as coinciding with 3R rules (reduction, recycling and reuse). In this work, a series of hydrochars (pristine, modified and composite) derived from invasive plants Alternanthera Philoxeroides(AP) were prepared and applied to the adsorption and co-adsorption of heavy metals (HMs) such as Pb(II), Cr(VI), Cu(II), Cd(II), Zn(II) and Ni(II). The results show MIL-53(Fe)-NH₂- magnetic hydrochar composite (M-HBAP) displayed a strong affinity for HMs, which the maximum adsorption capacity for HMs were 261.74 (Pb(II)), 252.50 (Cr(VI)), 180.92 (Cd(II)), 163.76 (Cu(II)) and 77.84 (Zn(II)) mg/g calculated by Langmuir model. This may be because the doping of MIL-53(Fe)-NH₂ enhanced the surface hydrophilicity of hydrochar, which allows hydrochar to disperse in the water within 0.12 s and possessed excellent dispersibility compared with pristine hydrochar (BAP) and amine-functionalized magnetic modified hydrochar (HBAP). Furthermore, the BET surface area of BAP was improved from 5.63 to 64.10 m²/g after doing MIL-53(Fe)-NH₂. M-HBAP shows a strong adsorption effect on the single HMs system (52-153 mg/g), while it decreased significantly (17-62 mg/g) in the mixed HMs system due to the competitive adsorption. Cr(VI) can produce strong electrostatic interaction with M-HBAP, Pb(II) can react with CaC₂O₄ on the surface of M-HBAP for chemical precipitation, and other HMs can react with functional groups on the surface of M-HBAP for complexation and ion exchange. In addition, five adsorption-desorption cycle experiments and vibrating sample magnetometry (VSM) curves also proved the feasibility of the M-HBAP application.

Background: Exploration of marine macroalgae poly-saccharide-based nanomaterials is emerging in the nanotechnology field, such as wound dressing, water treatment, environmental engineering, biosensor, and food technology. Main body: In this article, the current innovation and encroachments of marine macroalgae polysaccharide-based nanoparticles (NPs), and their promising opportunities, for future prospect in different industries are briefly reviewed. The extraction and advancement of various natural sources from marine polysaccharides, including carrageenan, agarose, fucoidan, and ulvan, are highlighted in order to provide a wide range of impacts on the nanofood technology. Further, seaweed or marine macroalgae is an unexploited natural source of polysaccharides, which involves numerous different phytonutrients in the outermost layer of the cell and is rich in sulphated polysaccharides (SP), SP-based nanomaterial which has an enhanced potential value in the nanotechnology field. Conclusion: At the end of this article, the promising prospect of SP-based NPs and their applications in the food sector is briefly addressed.

Water treatment (WT) is currently among the major areas of research due to the depletion of water resources and fearmongering regarding environmental pollution, which has compelled the upgrading of conventional WT technology towards recycling and reuse. This review aims to provide the current state of natural coagulants and their application in the purification of surface water as sufficient clean water is required for household needs, health security, and environmental safety. A thorough and systematic review of the existing literature was performed, and the information related to water treatment using natural coagulants was compiled from 237 articles under various sections using a computerized bibliographic search via PubMed, Scopus, Web of Science, Google Scholar, CAB Abstracts, and several websites. The work provides explicit information related to natural coagulants and their merits and limitations, outlines methods to increase their coagulation performance, and highlights their coagulation mechanism, efficacy, valorization potential, and sustainability. From the information obtained, it can be concluded that although chemical coagulants are efficient in WT, they are usually expensive, toxic, associated with health issues, and thus non-sustainable. A sustainable alternative is the use of natural coagulants, which are readily available, economical, easy to use, biodegradable, non-toxic, eco-friendly, effective, and generate lower sludge volumes. They work via an adsorption process that involves polymeric bridging or neutralization of the charge. The WT efficiency of natural coagulants ranges from 50–500 nephelometric turbidity units (NTUs), which is similar to chemicals. Thus, they can be deployed in WT regimes and can contribute to the health security of rural populations in developing countries. It is unfortunate that, despite the known benefits of natural coagulants, their acceptance, commercialization, and widespread industrial application across the globe are still low. Therefore, there is a need for more exhaustive investigations regarding the mode of action, adoption, and commercialization of natural coagulants as a sustainable alternative to chemicals for a circular economy.

The application of magnetic biochar (MBC) has attracted significant attention due to its recyclability and adsorption capacity for Hg from aqueous solutions. However, its applicability is still inadequate, relying on poor selectivity. Some chemical substances could improve the sorption capacity of MBC. This review offers an advanced technological route to modify-MBC composition with significant adsorption volume toward Hg. Non-polluting humic acid-sodium salts (Ha-Na) were proposed to optimize Fe3O4-modified biochar (FBC), while the pyrolyzed substrate for the initial biochar (BC) production originated from any agricultural biomass material. The non-polluting Ha-Na can improve the FBC-specific surface area, the number and structure of pores, moderate the pH and adsorb Hg(II) from aqueous solutions. Further, the interaction of three simple projected equation mechanisms is proposed for BC, FBC, and Ha-Na. BC modified with the support of Fe3O4 and optimized by Ha-Na can be applied to improve Hg(II) adsorption, while insights and future investigations are suggested. Graphical abstract

With social progress and industrial development, heavy metal pollution in water and soils environment is becoming more serious. Although biochar is a low-cost and environmentally friendly adsorbent for heavy metal ions, its adsorption and immobilization efficiency still need to be improved. As an upgraded version of biochar, modified biochar has attracted extensive attention in the scientific community. This review summarized the recent research progress on the treatment methods on heavy metal pollutants in water and soils using biochar. The features and advantages of biochar modification techniques such as physical modification, chemical modification, biological modification and other categories of biochar were discussed. The mechanism of removing heavy metals from soil and water by modified biochar was summarized. It was found that biochar had better performance after modification, which provided higher surface areas and more functional groups, and had enough binding sites to combine heavy metal ions. Biochar is a very promising candidate for removing heavy metals in environment. Furthermore, some high valent metal ions could be reduced to low valent metals, such as Cr(VI) reduction to Cr(III), and form precipitates on biochar by in-situ sorption-reduction-precipitation strategy. However, it is still the direction of efforts to develop high-efficiency modified biochar with low-cost, high sorption capacity, high photocatalytic performance, environmentally friendly and no secondary pollution in future.

From the perspective of treating wastes with wastes, bamboo sawdust was integrated with a hydroxyapatite (HAP) precursor to create engineered nano-HAP/micro-biochar composites (HBCs) by optimizing the co-precipitated precursor contents and co-pyrolysis temperature (300, 450, 600 °C). The physicochemical properties of HBCs, including morphologies, porosities, component ratios, crystalline structures, surface elemental chemical states, surface functional groups, and zeta potentials as a function of carbonization temperatures and components of precursors, were studied. Biochar matrix as an efficient carrier with enhanced specific surface area to prevent HAP from aggregation was desired. The sorption behavior of heavy metal (Cu(II), Cd(II), and Pb(II)) and pharmaceuticals (carbamazepine and tetracycline) on HBCs were analyzed given various geochemical conditions, including contact time, pH value, ionic strength, inferencing cations and anions, coexisting humic acid, and ambient temperature. HBCs could capture these pollutants efficiently from both simulated wastewaters and real waters. Combined with spectroscopic techniques, proper multiple dominant sorption mechanisms for each sorbate were elucidated separately. HBCs presented excellent reusability for the removal of these pollutants through six recycles, except for tetracycline. The results of this study provide meaningful insight into the proper integration of biochar–mineral composites for the management of aquatic heavy metals and pharmaceuticals.

Recently, metal–organic frameworks (MOFs), which are porous inorganic–organic hybrid materials consisting of metal ions (clusters or secondary building units) and organic ligands through coordination bonds, have attracted wide attention because of their high surface area, huge ordered porosity, uniform structural cavities, and excellent thermal/chemical stability. In this work, durian shell biomass carbon fiber and Fe₃O₄ functionalized metal–organic framework composite material (durian shell fiber-Fe₃O₄-MOF, DFM) was synthesized and employed for the adsorption removal of methylene blue (MB) from wastewater. The morphology, structure, and chemical elements of the DFM material were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscope (XPS) techniques. Adsorption conditions such as pH, adsorption time, and temperature were optimized. The adsorption isotherm and kinetics results show that the adsorption process of DFM material to MB is more in line with the Freundlich model and pseudo-second-order kinetic model. Using these models, the maximum adsorption capacity of 53.31 mg/g was obtained by calculation. In addition, DFM material could be easily reused through an external magnet and the removal rate of MB was still 80% after five adsorption cycles. The obtained results show that DFM composite material, as an economical, environmentally friendly, recyclable new adsorbent, can simply and effectively remove MB from wastewater.

In this study, bone char pretreated with hydrogen peroxide and traditional pyrolysis was applied to remove Cd²⁺ from aqueous solutions. After hydrogen peroxide pretreatment, the organic matter content of the bone char significantly decreased, while the surface area, the negative charge and the number of oxygen-containing functional groups on the bone char surface increased. After being pyrolyzed, the specific surface area and the negative charge of the material were further improved. The adsorption kinetics and isotherms of Cd²⁺ adsorption were studied, and the influence of solution pH and the presence of ionic species were investigated. The experimental results showed that the samples with lower crystallinity exhibited less organic matter content and more surface oxygen-containing functional groups, resulting in stronger adsorption capacity. After being treated with hydrogen peroxide and pyrolyzed at 300 °C, the maximum adsorption capacity of bone char was 228.73 mg/g. The bone char sample with the lowest adsorption capacity(47.71 mg/g) was pyrolyzed at 900 °C without hydrogen peroxide pretreatment. Ion exchange, surface complexation, and electrostatic interactions were responsible for the elimination of Cd²⁺ by the bone char samples. Overall, this work indicates that hydrogen peroxide-treated pyrolytic bone char is a promising material for the immobilization of Cd²⁺.

Resulting from the growing human population and the long dependency on fossil-based energies, the planet is facing a critical rise in global temperature, which is affecting all ecosystem networks. With a growing consciousness this issue, the EU has defined several strategies towards environment sustainability, where biodiversity restoration and preservation, pollution reduction, circular economy, and energetic transition are paramount issues. To achieve the ambitious goal of becoming climate-neutral by 2050, it is vital to mitigate the environmental footprint of the energetic transition, namely heavy metal pollution resulting from mining and processing of raw materials and from electronic waste disposal. Additionally, it is vital to find alternative materials to enhance the efficiency of energy storage devices. This review addresses the environmental challenges associated with energetic transition, with particular emphasis on the emergence of new alternative materials for the development of cleaner energy technologies and on the environmental impacts of mitigation strategies. We compile the most recent advances on natural sources, particularly seaweed, with regard to their use in metal recycling, bioremediation, and as valuable biomass to produce biochar for electrochemical applications.