Eliminating heavy metals from aqueous solutions continues to be of major environmental concern, primarily due to their non-biodegradable nature and hazardous effects. In this study, a Ca-modified low-temperature pine bark biochar (CaPB300) was developed as a sustainable and cost-effective adsorbent. The adsorption behavior of Cu(II) and Ni(II) in both single and binary systems was systematically investigated. Thermal treatment converted native carboxylic acid groups into deprotonated carboxylate (−COO−) groups, which acted as primary adsorption sites. The adsorption process was mainly governed by surface complexation, indicating a chemisorption-dominated mechanism. The Langmuir model demonstrated that in isolation, Cu(II) and Ni(II) demonstrated similar adsorption capacities at (56.85 and 55.88) mg/g, respectively. However, the introduction of a binary system significantly altered these figures to (65.20 and 11.45) mg/g for Cu(II) and Ni(II), respectively, confirming that when competing for available sites, Cu(II) outperforms Ni(II). In the binary system, Cu(II) was preferentially adsorbed over Ni(II) due to its stronger affinity toward carboxylate groups, leading to the formation of more stable surface complexes. Response surface methodology (RSM) was used to optimize the parameters for the adsorption process. The predicted removal efficiencies approached 100% for Cu(II) in both single and binary systems, while under optimized conditions, Ni(II) removal reached up to 99.39%. Overall, CaPB300 demonstrated efficient removal of Cu(II) and Ni(II), with pronounced selectivity toward Cu(II). These findings demonstrate the potential of CaPB300 as a cost-effective and sustainable adsorbent to treat multi-metal wastewater.
This study presents a composite modification design approach for developing a mechanically robust cement-based electrolyte/separator (CBE) through cellulose microfiber (CMF) reinforcement and in situ polymerization of polyacrylamide (PAM). Microstructural characterization confirmed successful in situ polymerization and physical interactions with cement hydration products without the formation of new crystalline phases, as supported by FTIR, XRD, and TGA. The CBE with 7% monomer achieved the highest ionic conductivity (15.93 mS/ cm) while maintaining a compressive strength of about 28.87 MPa. The cement-based structural supercapacitor (CSSC) incorporating the in situ polymerized electrolyte delivered an areal capacitance of 51.63 mF/cm2 at 0.4 mA/cm2. This corresponds to a 25.37% improvement at 0.4 mA/cm2, increasing to 53.41% at 1.0 mA/cm2 compared with plain cement, with greater energy density gains from lower resistance. The strong electrochemical performance enhancement is attributed to the hydrated pathways provided by the in situ polymerized PAM hydrogel network, which promote rapid ion transport when diffusion and kinetic limitations become more severe. The CSSC also showed 83% capacitance retention after 1000 cycles, highlighting the practical potential of this hierarchical composite design for building-integrated energy storage. Finally, this study demonstrates the importance of tailored electrolyte design in balancing electrochemical gains while preserving mechanical integrity, which remains a central challenge for cement-based energy storage materials.
Cement-based structural supercapacitors (CSSCs) offer a route to embed electrochemical energy storage directly in load-bearing infrastructure. This review focuses on cementitious-based supercapacitors by clearly separating and reconnecting two research directions: carbon cement electrodes (CCEs), where the cement matrix hosts percolated electronic networks, and cement-based electrolyte or separators (CBEs), where hydrated and polymer-modified cement act as ion-conducting scaffolds. Clear fabrication strategies and the working mechanisms that connect electronic conduction to charge storage in CCEs are examined, focusing on the formation and stability of conductive pathways as a function of filler type (single and hybrid fillers), dispersion strategy, electrode geometry (area and thickness), hydration control, porosity, and cracking, and on how these factors link microstructure to resistivity, capacitance, and mechanical strength. The evolution of CBEs is traced from simple alkaline pore-solution systems to polymer, redox-active, foamed, layered, and ice-templated architectures that decouple ionic conductivity from compressive strength and enable areal capacitances approaching those of non-structural solid-state devices. Reported cyclic voltammetry, galvanostatic charge–discharge, and impedance data are consolidated to clarify how pore topology, moisture state, and redox loading govern the balance between ionic conductivity, areal capacitance, energy and power densities, and compressive strength. These insights position cement-based supercapacitors as practical, scalable solutions for distributed energy storage in zero-energy buildings, where infrastructure itself becomes an active participant in energy management.
Rare earth elements (REEs) are critical for clean energy and digital technologies. However, their supply security remains uncertain. This review synthesizes the recent advances in REE recovery, focusing on membrane-based pressure-driven processes and selective chemical precipitation. Both commercial and laboratory-made membranes are examined, with an emphasis on operating factors such as pressure, pH, feed composition, and temperature. Size sieving and Donnan exclusion emerge as the dominant separation mechanisms, although fouling and low-pH stability continue to pose challenges. In terms of selective precipitation, common precipitants (e.g., carbonate, phosphate, and oxalate) and emerging organic and ionic liquid extractants are analyzed. Particular attention is given to factors influencing precipitation efficiency and selectivity, including precipitant and REE concentrations, solution pH, reaction time, and temperature, as well as additional variables such as stirring intensity, aging, and co-existing ions. The recovery mechanisms are further validated using microscopic, crystallographic, and spectroscopic evidence. Especially, the integration of membrane preconcentration with staged, pH-programmed precipitation proves promising, offering enhanced selectivity, reduced reagent demand, and high-purity REE products. In the future, sustainable recovery will depend on greener precipitants, regenerable membranes, pilot-to-demonstration-scale validation, and system designs aligned with sustainable resource management. These advances collectively demonstrate scalable and economically viable pathways for securing future REE supplies.
Electrochemical water splitting is an efficient and ecofriendly method for hydrogen production. Although Ptbased catalysts are the most widely used for the hydrogen evolution reaction (HER), their scarcity and high cost limit their applications. Therefore, the development of highly active catalysts based on nonprecious metals is required. In this study, a Mo-doped NiSe catalyst was synthesized on Ni foam (NF) as the Ni source via hydrothermal. The catalyst exhibited a two-dimensional nanoflower structure, and the presence of crystalline NiSe and Ni3Se2 was confirmed. Mo-doped NiSe achieved a current density of -10 mA cm- 2 at an overpotential of -148 mV in 1 M KOH, showing superior HER activity to that of NiSe (-194 mV), p-MoSe2 (-314 mV), and NF (-249 mV). Mo doping enhanced the activity by increasing the electrochemically active surface area and tuning the d-band of Ni. Long term stability tests over 6000 potential cycles reveal that the catalyst undergoes surface reconstruction while preserving its crystalline framework during this process. Mo is partially leached and readsorbed as high valent Mo6+, whereas Ni and Se remain largely unchanged. These results demonstrated that Mo-doped NiSe is a promising alkaline HER catalyst with excellent stability.
