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The study presents a facile and green approach to synthesizing crystalline TiO2 nanoparticles on a surface of biochar derived from abundantly available biomass waste, i.e., spent-coffee grounds (SCGs), via a simple sol-gel route. The biochar-TiO2 nanocomposite was used as an effective heterogeneous photocatalyst for the degradation and mineralization of priority pollutants, i.e., pentachlorophenol (PCP) in the aqueous phase. The physiochemical assessment of nanocomposite supports the efficient attachment of TiO2 to biochar, lowers the bandgap energy and particle size, and increases light absorption and durability for easy material separation after use. The radical scavenging experiments results revealed the dominance of superoxide radical anions (O2.-) followed by hydroxyl radicals (HO●) and photogenerated holes (h+) for the PCP degradation. Possible degradation mechanism and degradation pathways of PCP was also proposed. Besides, the nanocomposite material exhibited high stability for up to five cycles with negligible activity loss, further confirmed by the FT-IR analysis. Thus, biochar-TiO2 hybrid nanocomposite shows excellent photocatalytic activity for the degradation of organic pollutants in terms of performance metrics, which was far superior to the reported biomass-derived biochar/TiO2 materials and photocatalysts for PCP removal.

The goal of this study was to synthesize a chitosan-derived adsorbent that can be used in a coagulation–flocculation (CF) process for facile integration into existing water treatment processes. Therefore, an insoluble pyridinium-modified chitosan (Chi-Py) was prepared. Structural characterization was achieved with spectroscopy (FT-IR, 13C solids NMR, and X-ray photoelectron) methods and thermogravimetric analysis. Approximately 7% di-nitrobenzene and ca. 30% pyridinium moieties were incorporated into the chitosan framework via an adapted, moderate-temperature, Zincke reaction. The arsenic removal efficiency was evaluated by a coagulation-inspired methodology at pH 7.5, where the results were compared against CF systems such as pristine chitosan, FeCl3 and chitosan–FeCl3. The kinetic and van't Hoff thermodynamic parameters for arsenic removal were calculated. Arsenic adsorption was shown to be a spontaneous and exothermic process (ΔG = ?4.7 kJ mol?1; ΔH = ?75.6 kJ mol?1) with a 76% arsenic removal efficiency at 23 °C and 96% at 5 °C with a maximum effective adsorbent dosage of Chi-Py of 300 mg L?1. The adsorption process for Chi-Py followed pseudo-first order kinetics, where the pyridinium-modified chitosan adsorbent can be successfully employed similar to coagulant-like systems in conventional water treatment processes. In contrast to conventional adsorbents (1–2 g L?1), a dosage of only 300 mg L?1 was required for Chi-Py that offers greater sustainability and recycling of materials. This is contrasted with single-use conventional coagulants such as FeCl3 or binary FeCl3–chitosan CF systems.

One of the most agreed upon definitions of sustainability states that in order to achieve a sustainable development, the needs of the present must be met without compromising the ability of future generations to meet their own needs. Yet, the accomplishment of this target has its own challenges given the high growth of human population. All human beings require water, energy, and food in order to survive. The aim, then, is to satisfy these requirements through an adequate distribution of resources. The objective of this article is to explore, through a literature review, the application of the concept of sustainable design of the water–energy–food nexus. It is important to design supply chains that are as sustainable as possible while also fulfilling basic human needs.

Closing the loop in the flow of C, nutrients and water between agriculture, the human diet and sanitation services offers benefits for humanity across multiple platforms of public health, food security and climate mitigation. This study assesses these benefits by describing the hypothetical scenario of a global, ‘fully functional’ circular economy, in which 100% of C, N and P were recovered from human excreta and returned to agricultural soil. Crop nutrient demand is calculated and compared with that which could be recovered, and greenhouse (GHG) emissions from fertilizer production, fertilizer application and sanitation services are presented, as are freshwater availability and crop irrigation requirements. These are considered to analyse the broader effects of this circular economy that is driven by dietary nutrition demand on climate change, the provision of sanitation services and crop irrigation, in 2022 and with projections to 2030 and 2050. We find the capacity of the circular economy to deliver crop nutrients and mitigate GHG emissions varies by region. Some regions benefit from supplementing conventional mineral fertilizers with excreta-derived fertilizers, others from reducing GHG emissions from sanitation services through improved resource recovery rates. A hypothetical, fully functional circular economy that recovers all excreta nutrient C, N and P would reduce global GHG emissions from N and P mineral fertilizer production and application by 140 Tg CO2 equivalents (CO2 e) per year in 2022 (～12% of total emissions from mineral fertilizer production and application) and provide a maximum of 104 Tg C per year for sequestration in global cropland (～12% of estimated annual soil C sequestration potential). A portion of this sequestered C will return to the atmosphere via soil respiration, however, with co-benefits to other soil functions such as crop nutrient fertility. The maximum potential reduction in GHG emissions from sanitation services through these measures would bring reductions of 445 Tg CO2 e per year in 2022, rising to 562 Tg CO2 e in 2050. Our results provide evidence to guide specific regional policy on reducing GHG emissions, offsetting mineral fertilizer use and optimizing municipal water use using the circular economy.

Cr(VI) represents a worldwide issue due to its carcinogenicity and toxicity, and its removal from water/waste-water is of great relevance for the protection of human health and the environment. We here present an investigation of the adsorption and reduction properties towards Cr(VI) of two different kinds of industrial lignins: a kraft softwood lignin (HMW) and a hardwood lignin (EH) obtained by an enzymatic process. Moreover, we prepared and characterized an acetylated and a phosphorylated lignin starting from HMW, along with a lignin@magnetite hybrid material. The influence of various experimental parameters on the adsorption process, such as pH, contact time, quantity of lignin, Cr(VI) concentration and ionic strength, was evaluated. The best performances can be obtained at acidic pH (pH = 2). With an initial Cr(VI) concentration of 20 mg L?1 and a contact time of 24 hours, a quantitative Cr(VI) reduction was observed, accompanied by a removal of total chromium of up to 35% when HMW was used as the biosorbent. A comparison of the adsorption profiles of the different biosorbents highlighted the higher performance of EH, endowed with a higher surface area and characterised by a maximum adsorption capacity of about 208 mg g?1, while acetylation of the hydroxyl group led to a drop in the adsorption profile. The best fitting of the adsorption isotherm by using the Langmuir model suggests that a monolayer coverage of metal ions onto the homogeneous active sites of the lignin's surface better describes the interactions occurring at the biosorbent interface. Overall, this study demonstrates that technical lignins, and particularly EH hardwood lignin, are effective and economic materials that could be successfully employed in the Cr(VI) water remediation process.

Pyrolysis-assisted catalytic hydrogenolysis over Pd/C in anisole (phenyl methyl ether) at relatively high temperatures (>300 °C) can convert softwood lignin into aromatic monomers in >60 mol% yield (based on lignin aromatic rings). In this process, lignin is pyrolytically degraded to soluble intermediates prior to catalytic conversion, therefore the pyrolysis stage plays an important role in determining the yield and monomer composition. In this study, pyrolysis-assisted hydrogenolysis of coniferyl alcohol, which is a major pyrolysis product, and milled wood lignin isolated from Japanese cedar was investigated in various solvents, including water, methanol, toluene, hexane, and anisole, to clarify the solvent effects. The effects of the solvent on undesired side reactions were also explored. The results show that anisole is the best solvent for aromatic monomer production, but hexane is the best solvent for phenol production via demethoxylation. These findings provide insights that will facilitate the development of efficient methods for monomer production from lignin.

Nitrogen is a key nutrient source in agriculture, which has a crucial impact on crop productivity. Out of available nitrogen fertilizers, urea is identified as the major nitrogen source, accounting for ～60% of global use. However, due to the low nutrient usage efficiency of urea, it has become unsustainable, as 50–70% nitrogen applied is lost due to leaching, volatilization and nitrification, causing a series of environmental hazards and economic losses. Moreover, the recent global pandemic as well as war disrupt the food supply chain and fertilizer market. Here we used mechanochemistry to prepare a series of novel urea cocrystals that showed sustained-release behavior with significant improvement (～4 times), lower volatilization, and improved hydration stability compared to commercial urea. Therefore, the proposed urea cocrystal based fertilizer system demonstrates a potential sustained-release nitrogen source in agriculture where excessive use of fertilizer and nutrient loss can be minimised.

This review describes the recent research and development progress in the radical polymerization of bio-based monomers in aqueous dispersed media. The previous review on this subject was published in 2019 by S. Molina-Gutiérrez and coworkers (Green Chem., 2019, 21, 36). This topic is constantly evolving and improving because of the need for greener solutions to replace petroleum-derived monomers and more sustainable procedures to generate aqueous dispersions of polymers. For these reasons, we chose not only to update the previous review, but also to emphasize opportunities and constraints and to present considerations about green chemistry to outline the revolution that is arising.

Recovery of elemental copper, bismuth, tellurium, antimony and tin from thermoelectric generators (TEGs) is vital to recover the high content of critical metals and potential risk of environmental pollution as a result of incorrect disposal of TEGs and to enable the circular economy. In this work, aqueous choline chloride and calcium chloride hexahydrate brines were characterised and used in combination with copper(II) as an oxidising agent to leach copper and tin from TEGs. This permitted the Bi2?xSbxTe3 legs to be readily separated from the ceramic substrates by filtration. It was shown that at low chloride content, surface passivation and solubility of the oxidised species were the limiting factors towards oxidation, whereas solvent viscosity (mass transport) was the limiting factor at high chloride content. The copper(II) species formed in the different brines were determined via UV-vis spectroscopy. The redox potentials of the oxidising species were found to be significantly altered by choline chloride content, but not so much by calcium chloride hexahydrate content, suggesting variation in chloride activity within the different brines. The developed approach has been shown to be a viable and scalable method to recover high value critical metals from e-waste containing TEGs.

The rising interest in wearable devices has galvanized research into the development of flexible electronics. Flexible iontronics, devices that employ ions as charge carriers, have been accessed by employing ionic conductive hydrogels. While petroleum-based polymers have dominated this field, recently there is a drive towards renewable alternatives to develop more sustainable alternatives. This review focuses on the use of cellulose in ionic conductive hydrogels (IHCs) and their application in fabricating iontronics. The general structure and properties of cellulose and its derivatives are described, highlighting the inherent properties of the material that can be utilized to enhance the performance of IHCs. Subsequently, the basic theory behind ionic conduction is discussed, providing to the reader a brief overview of the origin, process and factors that influence ionic conduction. Thereafter, a discussion is presented on the major factors that influence the performance of ICHs and how the inherent properties of cellulose have been employed to improve the properties of these material. Finally, we discuss examples of devices in which the properties of the ionic conductor are enhanced by the presence of cellulose.