Activated Biocarbon from Paper Mill Sludge as Electrode Material for Supercapacitors: Comparative Performance Evaluation in Two Aqueous Electrolytes.

The valorization of a South African paper mill waste sludge into an activated biocarbon electrode material for energy storage application is reported. The valorization method is a two-step synthesis that comprises hydrothermal carbonization and NaOH activation of paper mill waste at 700 °C to produce activated biocarbon. The development of high porosity carbon material with a surface area of 1139 m2/g was observed. The synthesized biocarbon electrode exhibited good specific capacitance (C sp) values of 206 and 157 Fg-1, from a three-electrode cell in neutral (1 M Na2SO4) and alkali (3 M KOH) electrolytes, respectively. The electrolyte concentration purportedly has a considerable effect on specific capacitance. In both electrolytes, symmetric triangular curves in galvanostatic charge-discharge point to a quick charge-discharge process. Synthesized material testing with a two-electrode cell in 3 M KOH and 1 M Na2SO4 electrolytes, respectively, delivered specific capacitances of 125 and 152 Fg-1, with the corresponding energy densities of 17.4 and 21.1 Wh kg-1. The material had capacity retention efficiencies of 83 and 92% after 5000 cycles in 3 M KOH and 1 M Na2SO4 electrolytes, respectively. The electrode material performance of the activated biocarbon from paper sludge clearly shows its potential for electrochemical energy storage. The reported results present an exciting potential contribution of the pulp and paper industry toward the transition to green energy.

Fixed-bed operation for manganese removal from water using chitosan/bentonite/MnO composite beads.

In the present study, a new composite adsorbent, chitosan/bentonite/manganese oxide (CBMnO) beads, cross-linked with tetraethyl-ortho-silicate (TEOS) was applied in a fixed-bed column for the removal of Mn (II) from water. The adsorbent was characterised by scanning electron microscopy (SEM), Fourier transform infra-red (FT-IR), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) techniques, and moreover the point of zero charge (pHpzc) was determined. The extend of Mn (II) breakthrough behaviour was investigated by varying bed mass, flow rate and influent concentration, and by using real environmental water samples. The dynamics of the column showed great dependency of breakthrough curves on the process conditions. The breakthrough time (tb), bed exhaustion time (ts), bed capacity (qe) and the overall bed efficiency (R%) increased with an increase in bed mass, but decreased with the increase in both influent flow rate and concentration. Non-linear regression suggested that the Thomas model effectively described the breakthrough curves while large-scale column performance could be estimated by the bed depth service time (BDST) model. Experiments with environmental water revealed that coexisting ions had little impact on Mn (II) removal, and it was possible to achieve 6.0 mg/g breakthrough capacity (qb), 4.0 L total treated water and 651 bed volumes processed with an initial concentration of 38.5 mg/L and 5.0 g bed mass. The exhausted bed could be regenerated with 0.001 M nitric acid solution within 1 h, and the sorbent could be reused twice without any significant loss of capacity. The findings advocate that CBMnO composite beads can provide an efficient scavenging pathway for Mn (II) in polluted water.

Removal of fluoride from aqueous solution by polypyrrole/Fe3O4 magnetic nanocomposite.

Polypyrrole (PPy)/Fe(3)O(4) magnetic nanocomposite as a novel adsorbent was prepared via in-situ polymerization of pyrrole (Py) monomer using FeCl(3) oxidant in aqueous medium in which Fe(3)O(4) nanoparticles were suspended. The adsorbent was characterized by Attenuated Total Reflectance Fourier transform infrared spectroscope (ATR-FTIR), Brunauer-Emmet-Teller (BET) method, field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD). Magnetic property of the adsorbent was measured by electron spin resonance (ESR). Subsequently, the ability of the adsorbent to remove fluoride ions from aqueous solution was demonstrated in a batch sorption mode. Results reveal that the adsorption is rapid and that the adsorbent has high affinity for fluoride, which depends on temperature, solution pH and adsorbent dose. From equilibrium modelling, the equilibrium data is well described by Freundlich and Langmuir-Freundlich isotherms while the adsorption kinetics is described by the pseudo-second-order model. Thermodynamic parameters confirm the spontaneity and endothermic nature of the fluoride adsorption. Meanwhile, the fluoride adsorption proceeds by an ion exchange mechanism.