The two-electron (2e-) oxygen reduction reaction (ORR) for H2O2 electrosynthesis presents a sustainable alternative to the energy-intensive anthraquinone process. Single-atom catalysts as highly promising candidates for 2e-ORR. However, the overly strong adsorption of the key OOH* intermediate on single-atom sites (SAS) often leads to the undesired cleavage of the O-O bond, which becomes a key bottleneck in achieving high H2O2 selectivity. To circumvent this limitation, in this study, a composite of ZnO nanocrystals and ZnO3Cl SAS embedded in porous carbon (ZnSA-ZnO/PC) was designed and synthesized using a facile strategy. Operando spectroscopy and density functional theory (DFT) calculations revealed the regulation mechanism of ZnO nanocrystals on ZnO3Cl SAS. It optimized O2 activation at the ZnO3Cl SAS and attenuated the OOH* adsorption energy, thereby achieving superior catalytic performance. This synergistic configuration enables sustained H2O2 production in a gas-diffusion electrode flow reactor at a rate of 34.32 mol g-1 h-1 (17.16 mM h-1), with a Faradaic efficiency (FE) of over 80% during a 60 h operation at 250 mA cm-2. The direct accumulation of a 3.5 wt% H2O2 solution meets commercial disinfection standards. Moreover, the practical utility of the electro-synthesized H2O2 was demonstrated through effective antibacterial action against Staphylococcus aureus and the successful synthesis of benzamide from benzonitrile. This work provides an effective strategy for designing high-performance, non-precious metal electrocatalysts for scalable, sustainable H2O2 production.

Recent applications of low-field NMR in alkali-activated materials (AAMs) often adopt interpretation models developed for Portland cement systems, overlooking the distinct influences of paramagnetic/ferrimagnetic components and free-water redistribution. This study investigates how paramagnetic or ferrimagnetic component and free water distribution influence low-field nuclear magnetic resonance (LF-NMR) and proton density magnetic resonance imaging (PD-MRI) characterization of alkali-activated materials (AAMs). Blast furnace slag, fly ash, and steel slag were activated with NaOH solution at liquid-to-solid ratios of 0.45 and 0.5, and analyzed across top, middle, and bottom layers. Slurries prepared with less mixing water and CaO-rich raw materials exhibited negligible settling and uniform relaxation behavior, whereas those with higher water content and CaO-deficient raw materials showed pronounced stratification, resulting in distinct gradients in signal intensity. The results indicate that the LF-NMR data interpretation of relatively dilute system may be unreliable as the relaxation time of protons will be extended after they transfer from bottom to the top of the slurry. A preliminary method for assessing slurry suitability for LF-NMR characterization is proposed for future validation.

In this study, a low-cost and feasible crystal regulation of calcium carbonate (CaCO3) during steel slag (SS) carbonation and its consequent effects on carbonation kinetics, microstructure, mechanical properties, and heavy metal immobilization were systematically investigated. The results showed that NH4+ released from the hydrolysis of aluminum nitride (AlN) in secondary aluminum ash (SAA) promoted Aragonite nucleation, achieving Aragonite-dominated products under appropriate mixing ratios (10 %). Compared to Calcite, Aragonite enhanced the carbonation efficiency, micromechanical properties, interparticle connectivity, and pore structure of the material. Consequently, after 7 days, the 10#SAA sample exhibited a 26.8% higher carbonation efficiency and a 10 % greater compressive strength than the SAA-free control (0#SAA). SS inherently immobilizes exogenous Mn(II), Zn(II), and Cu(II) with nearly 100 % efficiency, while exogenous Cr(VI) immobilization (>96 % at 0.1 % loading) is governed by carbonate minerals. Owing to metastable nature and abundant lattice defects, Aragonite exhibits a higher Cr(VI) retention capacity than Calcite.

The potential of biochar as an alternative fuel for sintering is limited by its physicochemical disparities compared to fossil fuels. To address this, this study developed two combined processes by integrating hydrothermal carbonization (HTC) and pyrolytic carbonization (PC) for multi-stage regulation. The effects of process temperatures (HTC: 180/200/220 °C; PC: 400/500/600 °C) and sequences - specifically HTC followed by PC (HTC-PC) and PC followed by HTC (PC-HTC)-were systematically evaluated. Comparative tests at 600 °C showed HTC-PC biochar performed best: fuel ratio increased by 32.9%-49.9%, ash content decreased by 56.2%-70.3%, K (44.4-58.8%) and Na (31.6-67.6%) were effectively removed, with equilibrium moisture reduced by 13.5%-21.6%. It had excellent fixed carbon (71.9%-88.2 wt%), low ash (3.4%-7.2 wt%), high HHV (27.5-31.5 MJ/kg) and controlled metal content, whose combustion performance was comparable or superior to metallurgical fossil fuels. These findings provide important insights for optimizing biochar replacement rate in low-carbon sintering while maintaining sinter quality.

Owing to the reactivity between aluminates and CaCO3, carbonated steel slag (CSS) exhibits significant potential for utilization in calcium aluminate cement (CAC). The role of CSS in the mechanical properties, hydration characteristics, and microstructure development of CAC was investigated. The results showed that composite CAC pastes with CSS (CSS-CAC) exhibited excellent mechanical properties, and the compressive strength of the optimal CSS-CAC (CSS-20 samples) was 24.8 % and 28.0 % higher than that of CAC at 1 and 3 days, respectively. During hydration, CSS was involved in CAC hydration to form hemicarboaluminate (Hc) and monocarboaluminate (Mc), while the large specific surface area of CSS provided nucleation sites for the formation of hydration products, thereby enhancing the hydration efficiency of CaAl2O4 in cement. The reactivity and nucleation of CSS contributed to an increase in the interfacial strength between CSS particles and hydrated cement paste (HCP) sites, as well as a denser microstructure in HCP sites. Therefore, the HCP exhibited stronger micromechanical properties in CSS-CAC pastes with the increase of CSS content, and the elastic modulus of HCP gradually increases from 18 GPa to 102 GPa. However, the addition of CSS will introduce a large number of pores in the range of 0-100 nm, resulting in an increase in the total porosity of CSS-CAC samples. This research provides a new approach for the subsequent resource utilization of CSS and the low-carbon production of CAC.

Carbonation steel slag (CSS) has attracted growing attention as a sustainable precursor for supplementary cementitious material. But its reaction mechanisms and workability in alkali-activated systems remain poorly understood. Herein, ternary alkali-activated materials (AAMs) are prepared using CSS, fly ash (FA) and blast furnace slag (BFS) as precursors activated by sodium silicate (NS) and sodium hydroxide (NH), which causes strikingly different activation kinetics. In the NS-activated binder, Soluble silicate compounds undergo highly efficient polymerization reactions with Ca2+ ions dissolved from calcite, giving rise to a highly polymerized and compact N-(C)-A-S-H gel layer. NSC30 (NS+30 % CSS) achieves an unprecedented compressive strength of 152.1 MPa for curing 7 d, with harmless pores accounting for more than half of the total porosity. By contrast, the NH-activated binder exhibits more intense exothermic behavior with a higher paste viscosity, leading to the formation of short-chain C-A-S-H gels together with several unstable crystalline products. The high concentration of OH- in NH activators is detrimental to the polymerization of high-calcium CSS, whereas the by-product Ca (OH)2 may cause expansion. The life cycle assessment (LCA) reveals that the NSC30 binder achieves the lower carbon footprint (225.6 kg CO2-eq/t), a 36 % reduction relative to the NHC30. Overall, the CSS-NS route offers a balanced advantage in mechanical performance, dimensional stability and carbon reduction.

Steel slag, a major byproduct of the steel industry, poses a significant environmental challenge due to its low utilization rate and the risk of heavy metal leaching. Nevertheless, it is also a valuable reservoir of critical elements, such as calcium, phosphorus, and vanadium. This review provides a critical and comprehensive analysis of hydrometallurgical pathways to unlock the potential of steel slag as a secondary resource. We systematically evaluate conventional leaching methods (including acid, alkaline, and ammonium salt leaching) detailing their mechanisms, efficiencies, and environmental trade-offs. Beyond established techniques, the review explores emerging technologies, such as ultrasonic-assisted, microwave-assisted, and high-pressure leaching, which offer enhanced kinetics and a greener footprint. By synthesizing a vast body of literature, this work establishes a clear comparative framework based on operational parameters and extraction performance. Finally, we outline the pressing challenges and prospects, emphasizing the imperative for integrated approaches that advance the steel industry toward a circular economy. This review serves as a strategic guide for researchers and engineers aiming to transform steel slag from a waste liability into a valuable asset.

Abstract Steel slag, a major industrial waste, was converted into iron oxide nanoparticles (IONPs) via a plant-extract-mediated synthesis using Ginkgo biloba leaf extract. The resulting nanomaterial demonstrated high effectiveness as an adsorbent for the model cationic dye methylene blue, with a capacity of 294.97 mg/g and removal efficiency >98%. Adsorption followed pseudo-second-order kinetics and the Freundlich isotherm, with DFT simulations indicating charge-transfer-enhanced electrostatic interactions as the key mechanism. The process adopts a circular economy perspective by recovering iron as a nano-adsorbent, concentrating co-leached Mn/Mg into a manageable residue, and directing the primary CaSO4/SiO2-rich residue toward construction applications. While the nanoparticle synthesis step incorporates green chemistry principles, the study highlights the integration of hydrometallurgical waste processing with bio-inspired nanomaterial fabrication as a sustainable resource management strategy.

This study presents a transformative zero-waste paradigm for up-cycling steel slag (SS) which is an abundant industrial waste, by strategically deconstructing it into two valuable products. The established process involves the targeted sulfuric acid leaching of SS to separate its major components: iron ions and calcium. The iron-rich leachate serves as a precursor for the plant-mediated synthesis of α-Fe2O3/SiO2 nanocomposites using Gingko biloba leaf extract, while the solid residue is transformed into gypsum (CaSO4·2H2O), a huge applicable material in construction and agriculture. Optimization of methylene blue (MB) adsorption using the Taguchi method achieved an experimental equilibrium capacity of 37.03 mg/g under the investigated conditions. The adsorption behavior was best described by the pseudo-second-order kinetic model and the Freundlich isotherm model, indicating dominant chemisorption on a heterogeneous surface. The Freundlich constants (KF = 75.5 (mg/g)(L/mg)1/n and n = 2.04) confirmed strong adsorption affinity and favorable adsorption characteristics. A Langmuir monolayer capacity of 102.04 mg/g was estimated from model fitting. Density functional theory (DFT) and molecular mechanics simulations provided atomistic-level confirmation of a strong, exothermic interaction between methylene blue (MB) and the Fe2O3 surface, albeit moderated in an aqueous environment. Furthermore, the nanocomposite showed remarkable stability, retaining over 70

Non-sintered ceramsite (NC) is generally regarded as a low-carbon lightweight aggregate, but its production still relies on carbon-intensive binders, compromising its environmental benefits. Carbide slag (CS), a highly alkaline solid waste, can serve as an alternative binder. However, the low liquid-to-solid ratio in NC preparation makes it difficult to fully exploit the alkaline activation potential of CS, which hinders the development of NC strength. Herein, CS is redefined as a dual-functional component, acting simultaneously as an alkaline activator and an in-situ calcium source for carbonation. On this basis, CS is combined with coal-based solid waste to produce fully solid-waste-based NC. The results indicated that inert coal gangue (CG) particles serve as a load-bearing framework, while the hydration products, ettringite (AFt) and C-A-S-H gel, refined the pore structure. Calcite formed in situ during natural carbonation, further filling the pores and densifying the matrix. The coupled effect of hydration and natural carbonation significantly enhanced the overall performance of the NC. The crushing value of the optimized NC was 10.4%, which was 40%–77% lower than that of other samples. Furthermore, the CO2 uptake capacity of 85.5 mg/g was achieved, while the carbon footprint during the production phase was 14.9 kg CO2-eq/t. When applied in mortar, the prepared NC slightly reduced compressive strength but improved thermal insulation performance, with a 61.0% reduction in thermal conductivity. These results highlight the low-carbon and functionalized potential of the prepared NC.

Synthesis of porous geopolymers from industrial byproducts as sustainable adsorbents provides an encouraging pathway for both carbon mitigation and wastewater treatment. In this study, biochar, fly ash, and steel slag were utilized as raw materials to synthesize porous geopolymers and compare their adsorption performance before and after carbonation. Batch adsorption experiments were conducted at an initial methylene blue (MB) dye concentration of 100 mg/L, an adsorbent dosage of 3 g/L, neutral pH, and room temperature, with a contact time of 60 min. The results show that, within 60 min, the MB removal efficiency for non-carbonated porous geopolymer (NC-GP) and carbonated porous geopolymer (C-GP) was 82.709% and 90.716%, respectively, and achieved the adsorption capacity of 19.308 mg/g for NC-GP and 22.661 mg/g for C-GP. Characterization techniques such as XRD, FTIR, TG, BET, and SEM were used to analyze the geopolymer samples. Adsorption experiments revealed the successful removal of MB dye by both geopolymers, with the Freundlich isotherm and pseudo-second-order kinetic models being the perfect fit for the process. Thermodynamic analysis proved that the process was spontaneous and exothermic with enthalpy change (Delta H degrees) of -1551.252 J/mol and -3783.174 J/mol for NC-GP and C-GP, respectively. The MB uptake by both geopolymers was facilitated by adsorption mechanisms, including electrostatic attractions, hydrogen bonding, and it-it interactions.The enhanced adsorption performance of the C-GP demonstrates the function of carbonation in improving adsorption efficiency while also supporting the sustainable use of industrial byproducts and carbon mitigation.

Natural products have been widely used as additives of building materials. In this work, we explored the impact of dried okra mucilage (DOM) on the hydration and setting time of blast furnace slag (BFS). DOM acts as a plasticizer and retarder, enhancing the fluidity of the activated BFS paste and extending setting times at a concentration of only 0.5 parts per thousand. This addition preserves the alkaline environment, facilitating comparable compressive strength. Thermogravimetric analysis indicates that DOM delays the formation of C-(A)-S-H gel and hydrotalcite. This inhibitory effect on calcium- and magnesium-containing hydration products is further confirmed by solid-state NMR and IR spectroscopy. The in-situ low-field NMR results revealed the evolution of water bleeding in the early hydration stage, which contributed to the understanding of the final shrinkage of the hardened paste. These findings suggest DOM a promising natural retarder for alkali-activated BFS, potentially optimizing its workability and hydration in construction applications.

Porous alkali-activated fly ash (PAA-FA) is a sustainable building material, but its low compressive strength limits application. This study demonstrates that incorporating polyvinyl alcohol (PVA) fibers effectively enhances mechanical properties, with a 55% increase in compressive strength (from 1.1 MPa to 1.7 MPa) at an optimal 2.0 wt.% and 3 mm length. Crucially, fiber-matrix interfacial adhesion, governed by surface hydrophilicity, was identified as the key reinforcement mechanism. Hydrophilic PVA fibers formed strong bonds with the matrix, while hydrophobic polypropylene (PP) fibers reduced strength. Surface modification to increase PP fiber hydrophilicity successfully improved composite strength to 1.5 MPa, confirming this mechanism. Furthermore, fiber characteristics directly tailored the porous structure: hydrophilic fibers increased slurry viscosity, yielding finer pores and a 77% higher specific surface area, whereas hydrophobic fibers created interconnected pores, enhancing sound absorption. This work quantifies the critical role of fiber type, dosage, length, and surface chemistry, providing a strategic approach to mechanically strengthen PAA-FA and tailor its functional properties for specific structural and acoustic applications.

The conversion from metastable phase to stable phase in calcium aluminate cement (CAC) caused by temperature increase can lead to an increase in porosity and a decrease in compressive strength. This study investigated the effects of carbonated steel slag (CSS) on the hydration, microstructure, and resistance to temperature fluctuations of CAC at temperatures ranging from 20 degrees C to 70 degrees C. The results showed that the incorporation of CSS leads to the formation of carbonate-AFm (or AFt) phases (hemicarboaluminate (Hc) and monocarboaluminate (Mc)). The increase of CSS content promotes the hydration of CA and CA2 to Hc and Mc (Hc/Mc), and weakens the hydration to C3AH6 and AH3 at 70 degrees C. Therefore, the impact of the conversion from CAH10 phase to C3AH6 phase on CAC is weakened. As the CSS content increases from 0 to 40 %, the loss of compressive strength of the samples decreases from 45.7 % to 10.4 % at 70 degrees C for 7 days, corresponding to a 77.2 % increase in temperature fluctuation resistance. Meanwhile, the addition of CSS can alleviate the increase in pore volume of CAC at 70 degrees C, and even lead to a decrease in CSS-40 sample.

Due to low energy input, non-sintered lightweight aggregates (NLAs) attracted lots of attention. Generally, NLAs with high porosity are conducive to acoustic absorption and thermal insulation but compromise mechanical properties. To overcome the negative correlation between porosity and mechanical strength, accelerated carbonation was utilized to optimize the pore structure and mechanical strength of porous NLAs. The pore structure changes of porous NLAs from gel pores to macropores were comprehensively studied. Regarding gel pores and transition pores, the leaching of Ca2 + in C-(N)-A-S-H gels leads to the polymerization and shrinkage of silica-aluminate chains, increasing the proportion of gel pores and transition pores. For macropores, leached Ca2+ reacted with CO2 to form calcite on the pore wall refining pore size and improving closure, reducing the proportion of macropores. The optimized pore structure enhanced the mechanical properties of porous NLAs, achieving a bulk density of 626.78 kg/m3 and cylinder compressive strength of 3.26 MPa. Notably, carbonated porous NLAs facilitated the acoustic absorption of the high-frequency bands while maintaining a thermal conductivity of 0.265 W/(m & sdot;K), and showed an effective immobilization of heavy metals. The feasibility of the application of porous NLAs was verified by lightweight aggregate concrete production, achieving a density class of 1600 kg/m3 and a compressive strength of 26.59 MPa.

Porous materials have a wide range of applications in the adsorption of pollutants. In this study, porous geopolymer (PG) was prepared by using steel slag and fly ash as raw materials. The changes in the mechanical properties, microstructure, and methylene blue (MB) removal rate of PG caused by carbonation were observed. The results showed that the filling of CaCO3 and the increase of polymerization degree led to the increase of PG compressive strength during carbonation, and the compressive strength of carbonated PG reached 2.27 MPa. According to BET and XPS results, carbonation resulted in an increase in the specific surface area and surface hydroxyl functional groups of PG. Compared to non-carbonated PG, there was a 34% increase in the removal rate and adsorption capacity of MB. The maximum adsorption capacity of MB by carbonated PG was 27.61 mg/g. Additionally, FTIR analyses suggested that the electrostatic interactions and hydrogen bonding were the primary dye adsorption mechanisms, and the MB adsorption by carbonated PG conformed to fit the Freundlich isotherm and pseudo-second-order kinetic models.

Pharmaceutical residues in the environment and their transformation mechanism are important challenges in environmental pollution research. The present study investigated the transformation mechanisms and reaction kinetics of oxazepam, a representative of benzodiazepine pharmaceutical, with two typical water treatment oxidants including HOCl and ∙OH in aqueous solution through theoretical calculations and experimental verification. The results showed that oxazepam is a chiral molecule with two enantiomers in equal proportions. The reactions between oxazepam and HOCl can be classified into Cl-substitution, OH-substitution, and bond-fission reactions. Among these substitutions, the Cl-substitution reaction at the N23 site was most likely to occur. The bond-fission reactions were predominated by the cleavage of the C27-N29 bond, which could lead to further bond cleavage reactions. The reactions between oxazepam and ∙OH involved the addition and H-abstraction pathways, with the addition reactions at the C5, C13, and C17 sites being the top three major reaction pathways. The kinetics rate constants obtained by the density functional theory (DFT) calculation were 0.16 and 1.78 × 1011 M-1 s-1 for the reactions of oxazepam with HOCl (kHOCl, M-1 s-1) and ∙OH (k·OH, M-1 s-1) respectively, which are basically consistent with the experimental results. This comprehensive understanding of the reaction mechanisms of oxazepam with HOCl and ∙OH based on quantum chemical calculations is crucial for exploring the chlorination and advanced oxidation of benzodiazepine pharmaceuticals.

As one of the essential elements for life activities, phosphorus is largely available in human urine. Non-sintered ceramsite is environmentally friendly with low energy input and controllable pore structure, which is considered to be an ideal adsorbent for phosphorus recovery. This study used fly ash (FA), cement (OPC) and expanded perlite (EP) as raw materials to synthesize non-sintered porous ceramsites with different pore structures and recycled phosphorus from simulated urine. The produced ceramsites showed excellent phosphorus adsorption performance (2.25 mg/g adsorption capacity and 89.4 % removal efficiency). The adsorption performance could be affected by the particle size of perlite, initial phosphorus concentration, temperature and pH. The kinetic and isothermal adsorption conformed to the pseudo-first-order model and the Langmuir model, respectively. The main adsorption mechanism is dominated by physical adsorption and synergized by chemical adsorption. By analyzing the phase composition, microstructure, chemical bond, binding energy and pore structure of the produced ceramsites by XRD, SEM, FT-IR, XPS and MIP, the phosphorus adsorption process was proposed as phosphorus diffusion in pore structure, chemical precipitation and ligand exchange. The adsorption of phosphorus over ceramsite as an alternative phosphorus fertilizer promoted wheat seed germination and seedling growth.

The traditional chemical vapor deposition (CVD)graphene transfer process generates a large amount of solvent waste, posing a significant sustainability challenge. To address this, we designed a Cyclic Cleaning Multi-Chamber (CCMC) system. Inspired by Soxhlet extraction, the CCMC enables closed-loop solvent recycling through integrated distillation, condensation, and reflux mechanisms. Experimental results show that the system effectively removes poly(methyl methacrylate) (PMMA) residues from transferred graphene without damaging its structural integrity, a finding confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The CCMC system achieves a solvent recovery efficiency of over 98% across 25 cycles using acetone, significantly reducing solvent consumption compared to conventional methods. While providing this substantial environmental benefit, the energy demand remains moderate, increasing by only about 15 kWh. These results position the CCMC as a scalable, eco-friendly solution for the semiconductor and nanomaterial industries, promoting the broader adoption of sustainable manufacturing practices.

A reliable catalyst carrier is essential in heterogeneous persulfate advanced oxidation technology. Compared with the common catalyst carriers, porous geopolymer (PG) has the advantages of green synthesis, remarkable structure, excellent mechanical property and good stability. In this study, a Cu loaded and fly ash based porous geopolymer (Cu-PG) was successfully synthesized by a microwave-assisted impregnation method. By activating PMS, the produced Cu-PG degraded SMX effectively at a pH range of 7-11. The optimal SMX degradation performance (91.9 % removal rate) was with 2 g/L Cu-PG and 1 mM PMS at pH = 11 within 90 mins. During the degradation process, radicals (SO4 & sdot;-, & sdot;OH, O2 & sdot;-) and nonradicals (1O2, high-valent metals) pathways were identified by using EPR, quenching experiment, and HPLC. Cu (III) was considered as a crucial factor in the oxidation process of PMS/Cu-PG systems under alkaline condition. What's more, the cycling processes of Cu(I)/Cu(II)/Cu (III) in the PMS/Cu-PG system were proposed. In addition, LC-MS analysis suggested there were 6 possible degradation pathways in the PMS/Cu-PG systems. Environmental implication: As a graininess catalyst, Cu-PG exhibited good reusability. The practical application of Cu-PG in wastewater treatment could promote the reuse of fly ash, which benefits environmental sustainability and reduces catalyst costs.