Synergistic adsorption of methylene blue with carrageenan/hydrochar-derived activated carbon hydrogel composites: Insights and optimization strategies

The study explores the use of hydrochar-derived activated carbon (AC) to improve the adsorption capacity and mechanical properties of carrageenan (CAR) hydrogel beads. Four distinct samples, with carrageenan to activated carbon ratios of 1:0 (CAR), 2:1 (CAC2), 4:1 (CAC4), and 10:1 (CAC10), were prepared. These polymeric beads underwent comprehensive evaluation for their methylene blue (MB) adsorption capacity, gel content (GC), and swelling ratio (SR). Increasing activated carbon content up to 50 % of carrageenan mass significantly enhanced GC and SR by 20.57 % and 429.24 %, respectively. Various analytical techniques were employed to characterize the composites, including FTIR, XRD, Raman Spectroscopy, BET, SEM, and EDS-Mapping. Batch adsorption tests investigated the effects of pH, contact time, dye concentration, and temperature on MB adsorption. Maximum adsorption capacities for CAR, CAC10, CAC4, and CAC2 were 475.48, 558.54, 635.93, and 552.35 mg/g, respectively, under optimal conditions. Kinetic models (Elovich and pseudo-second-order) and isotherm models (Temkin for CAR and Freundlich for CAC10, CAC4, and CAC2) fitted well with the experimental data. Thermodynamic analysis showed spontaneous, exothermic MB adsorption. Primary mechanisms include electrostatic attraction, hydrogen bonding, n-π, and π-π stacking. The study highlights enhanced adsorption capacity of carrageenan hydrogel via carrageenan/activated carbon composites, providing cost-effective wastewater treatment.

Surface migration of Pb(II) from water and soil using an aerogel/graphite felt primary cell system

To develop a zero energy consumption electrokinetic remediation method of Pb(II) in water and soil, a primary cell system was constructed via synergistic effects of the electromigration, ion exchange, precipitation and hydrogen bond. The primary cell system used cathode of calcium alginate aerogel/graphite felt (CAA/GF) and another piece of CAA/GF was placed on the top of the water and soil. Thus the electric field in the system could drive positively charged Pb(II) towards the top of and thus Pb(II) was surface migrated, promoting removal of Pb(II). This system achieved Pb(II) removal efficiency of 97.8% and maximum power density of 32.1 mW m^-2. Additionally, the CAA/GF presented a good reusability. This work provides a promising and facile method to remove heavy metals from water and soil, which might have a huge application prospect.

Multi-component adsorption of Pb(II), Cd(II) and Ni(II) onto microwave-functionalized cellulose: Kinetics, isotherms, thermodynamics, mechanisms and application for electroplating wastewater purification

Herein, microwave-functionalized cellulose derived from rice husk was cost-effectively prepared and employed for Pb(II), Cd(II) and Ni(II) elimination in mono- and multi-component systems. Benefiting from microwave irradiation, the functionalized process was achieved in 6.5 min and the resultant RH_MW-X possessed remarkably high adsorption capacities of 295.20 mg/g for Pb(II), 151.51 mg/g for Cd(II) and 72.80 mg/g for Ni(II) within the equilibrium time of 30 min. Noticeably, the metal ions adsorption rate and capacity in binary and ternary systems were lower than that of unary systems. The coexistence of Cd(II) and Ni(II) significantly slowed down the Pb(II) adsorption in binary and ternary systems, while Pb(II) exhibited the most obvious influence on the metal ions uptake in the multi-component systems. FT-IR and XPS results revealed that both ion exchange and chelation were functioned in the metal ions uptake, while physical interaction was also involved in the adsorption process. Moreover, the RH_MW-X possessed favorable recyclability with slight adsorption efficiency decline during five cycles in different systems. Particularly, the RH_MW-X could effectively purify actual industrial wastewater containing Pb(II), Cd(II) and Ni(II) for meeting regulatory requirements. This work facilitates the omnidirectional improvement of adsorbents for the de-pollution of practical heavy metals wastewater.

A combined system of microwave-functionalized rice husk and poly-aluminium chloride for trace cadmium-contaminated source water purification: Exploration of removal efficiency and mechanism

Cadmium is highly poisonous to mammals and related water pollution incidents are increasing world-widely. Here, the clean-up of trace Cd(II) by a combined process of microwave-functionalized rice husk (RH_MW-M) and poly aluminium chloride (PAC) was investigated for the first time, with the exploration of removal mechanism and efficacy. Microwave irradiation was found to be a new approach to achieve the functionalized procedure, which could decrease the processing time from 2.5 h to 390 s with the Cd(II) uptake of the outcome product soaring from 137.16 mg/g to 191.32 mg/g. The ultra-rapidly prepared RH_MW-M exhibited a fast adsorption equilibrium within 30 min over a wide pH range of 5.0-8.0, and the FT-IR and XPS studies confirmed that both ion exchange and chelation were functioned in the Cd(II) uptake process. Controlled by the turbidity threshold of drinking water treatment plant, the feasible dosage of RH_MW-M in the absence and presence of 30 mg/L PAC increased from 30 to 760 mg/L, which could effectively deal with the trace Cd(II) at the concentration from 33 μg/L up to 0.933 mg/L, exhibiting much better performance than traditional alkali precipitation. Predictably, this simple and scalable RH_MW-M/PAC system could afford a promising end-of-pipe solution for heavy-metal contamination.