Green magnetic carbon/alginate biocomposite beads from iron scrap waste for efficient removal of textile dye and heavy metal.

The circular economy can help enhance the value of industrial waste and remediate the environment. This study considers the application of iron scrap from steel production as a free resource to produce magnetic adsorbent beads to remove methylene blue dye and lead (II) ions from wastewater. Composite beads were prepared by incorporating iron scrap and activated carbon into a calcium alginate gel using a simple 'mix and drop' synthesis. The optimized magnetic beads were stable and offered a large specific surface area. The maximum adsorption capacity of the adsorbent, calculated from the Langmuir isotherm model, was 476.19 mg g-1 for methylene blue and 163.93 mg g-1 for lead (II) ions. This study places emphasis upon the zero-waste principle and employs a scalable synthetic approach for the conversion of waste iron scrap into an adsorbent material capable of delivering significant environmental benefits.

Green and sustainable zero-waste conversion of water hyacinth (Eichhornia crassipes) into superior magnetic carbon composite adsorbents and supercapacitor electrodes.

Troublesome aquatic weed, water hyacinth (Eichhornia crassipes) was converted into solid and liquid fractions via green and energy-saving hydrothermal carbonization (HTC). The solid product, hydrochar, was employed as a precursor to prepare magnetic carbon materials by simple activation and magnetization using KOH and Fe3+ ions, respectively. The obtained magnetic adsorbent possessed good magnetic properties and presented outstanding capacities to adsorb methylene blue (524.20 mg g-1), methyl orange (425.15 mg g-1) and tetracycline (294.24 mg g-1) with rapid adsorption kinetics even at high concentrations (up to 500 mg L-1), attributed to high specific surface area and mesopore porosity. Besides the solid hydrochar, the water-soluble liquid product was used to fabricate carbon-based supercapacitors through facile KOH activation with a considerably lower KOH amount in comparison to conventional activation. The supercapacitor electrode made from activated liquid product possessed an extremely high specific surface area of 2545 cm2 g-1 and showed excellent specific capacitance (100 F g-1 or 50 F cm-3 at 1 A g-1) and good retention of capacitance (92% even after 10 000 cycles). This work demonstrated that both solid and liquid HTC fractions from this bio-waste can serve as effective sources to prepare functional carbon materials, making this approach a sustainable zero-waste biomass conversion process.

Magnetic carbon composites with a hierarchical structure for adsorption of tetracycline, prepared from sugarcane bagasse via hydrothermal carbonization coupled with simple heat treatment process.

Sugarcane bagasse, an agricultural waste, was successfully converted into novel magnetic carbon composites by low temperature hydrothermal carbonization at 230°C for 24h, followed by heat treatment at 400°C for only 1h in air. Effects of NaOH and iron loading on the chemical properties of the composites were studied. In addition, various techniques were employed to investigate the physicochemical properties of the composites. Adsorption kinetics and isotherms were investigated with tetracycline (TC) for the magnetic composites. The magnetic carbon composite exhibited 48.35mg/g maximum adsorption capacity and was highly stable chemically and mechanically, with also good magnetic properties. The adsorption of TC by the magnetic adsorbent was mainly attributed to H-bonds and π-π interactions. The results indicate that waste sugarcane bagasse from the sugar industries can be efficiently transformed to a magnetic adsorbent for TC removal via a facile environmentally friendly method.