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This study utilized a facile and scalable one-pot wet impregnation method for Hg(II) adsorption to prepare sulfur-anchored palm shell waste activated carbon powder (PSAC-S). The experimental results revealed that the sulfur precursors promote the surface charge on the PSAC and enhance Hg(II) removal via the Na 2 S > Na 2 S 2 O 4 > CH 3 CSNH 2 sequence. PSAC-S prepared using Na 2 S had significant Hg(II) sorption efficiencies, achieving a maximum sorption capacity of 136 mg g−1 from the Freundlich model. Compared to PSAC, PSAC-S had an enhancement in Hg(II) sorption behavior for heterogeneous interactions with sulfur. PSAC-S also demonstrated high Hg(II) sorption capacities over a wide range of solution pH, while ionic strength had an insignificant impact on Hg(II) removal efficiencies. Through various spectroscopic analyses, we identified the mechanisms of Hg(II) removal by PSAC-S as electrostatic interactions, Hg-Cl complexation, and precipitation as HgSO 4. Moreover, PSAC-S unveiled high adsorption affinity and Hg(II) stability in actual groundwater (even in µg L−1 level). These overall results show the potentials of PSAC-S as an alternative, easily scalable material for in-situ Hg(II) remediation. [Display omitted] • A facile and scalable preparation method of PSAC-S is demonstrated. • PSAC-S prepared by Na 2 S has the highest Hg(II) sorption capacity. • PSAC-S exhibits stable Hg(II) adsorption in groundwater after pH adjustment. • The main mechanisms are electrostatic interactions, Hg-Cl complexation, and precipitation. [ABSTRACT FROM AUTHOR]

• Mg-Fe-LDH embedded with PAM/PVA for As(III)/As(V) removal was studied for the first time. • PAM 40 /PVA 30 -LDH has higher stability in aqueous phase compared to Mg-Fe-LDH • PAM/PVA delaminated the Mg-Fe-LDH structures and enhances As(III)/As(V) sorption. • Hydrogen bonding, ion exchange of SO 4 2− and complexation are the dominant mechanism for As(III)/As(V) removal. Controlling the particle size and aggregation of nanosheet layers in layered double hydroxides (LDHs) is critical for their application. Herein, we report the preparation of Mg-Fe LDH through a co-precipitation method. The LDH was embedded using polyacrylamide (PAM) and polyvinyl alcohol (PVA; the LDH was designated as PAM/PVA-LDH) for As(III) and As(V) removal. We found that doping with 0.3 mL PVA (2 g L-1) and 0.4 mL (20 g L-1) PAM solution delaminated the nanosheet layers of 1 g of the LDH (PAM 40 /PVA 30 -LDH) and restructured the crystal phase from monoclinic to orthorhombic. This increased the surface area and pore volume. Furthermore, PAM 40 /PVA 30 -LDH exhibited higher affinity for As(III) and As(V) removal with maximum adsorption capacities of 14.1 and 22.8 mg g−1, respectively, compared to LDH alone with adsorption capacities of 7.1 and 7.9 mg g−1, respectively. It was found that the highest adsorption capacities of As(III) and As(V) using PAM 40 /PVA 30 -LDH occurred at pH ∼7 and pH 2.5, respectively. X-ray photoelectron spectroscopy analysis revealed that the removal of As(III) and As(V) on PAM 40 /PVA 30 -LDH was mainly attributable to ion exchange with intercalated SO 4 2-, hydrogen bonding, and complexation mechanisms. These findings illustrate that PAM 40 /PVA 30 -LDH would be an excellent adsorbent for the remediation of arsenic-polluted wastewater. [ABSTRACT FROM AUTHOR]

In this study, palm shell activated carbon powder (PSAC) and magnesium silicate (MgSiO 3) modified PSAC (MPSAC) were thoroughly investigated for fluoride (F−) adsorption. F− adsorption isotherms showed that PSAC and MPSAC over-performed some other reported F− adsorbents with adsorption capacities of 116 mg g−1 and 150 mg g−1, respectively. Interestingly, the MgSiO 3 impregnated layer changed the adsorption behavior of F− from monolayer to heterogeneous multilayer based on the Langmuir and Freundlich isotherm models verified by chi-square test (X2). Thermodynamic parameters indicated that the F− adsorption on PSAC and MPSAC was spontaneous and exothermic. PSAC and MPSAC were characterized using FESEM-EDX, XRD, FTIR and XPS to investigate the F− adsorption mechanism. Based on the regeneration tests using NaOH (0.01 M), PSAC exhibited poor regeneration (<20%) while MPSAC had steady adsorption efficiencies (∼70%) even after 5 regeneration cycles. This is due to highly polarized C–F bond was found on PSAC while Mg–F bond was distinguished on MPSAC, evidently denoting that the F− adsorption is mainly resulted from the exchange of hydroxyl (-OH) group. It was concluded that PSAC would be a potential adsorbent for in-situ F− groundwater remediation due to its capability to retain F− without leaching out in a wide range pH. MPSAC would be an alternative adsorbent for ex-situ F− water remediation because it can easily regenerate with NaOH solution. With the excellent F− adsorption properties, both PSAC and MPSAC offer as promising adsorbents for F− remediation in the aqueous phase. • MgSiO 3 impregnated on PSAC for fluoride removal was studied for the first time. • MPSAC showed higher fluoride adsorption capacities compared to PSAC. • Anions inhibited F− adsorption with the following sequence: Cl− < NO 3 − < SO 4 2-. • PSAC had stable sequestration capacities of fluoride due to strong C–F bond formation. • MPSAC had high regeneration capacities for ex-situ fluoride treatment using NaOH. [ABSTRACT FROM AUTHOR]

• PSAC under UVC 365 irradiation exhibits higher production of O 2 • due to slower e−/h+ recombination than other light sources. • The O 2 • generation from oxygen vacancies associated Si1+ is detected by using EPR spin trapping. • A strong correlation between the content of oxygen vacancies and Si1+ in PSAC and photocatalysis was obtained. • The continuous-flow column of PSAC under UVA 365 irradiation had a > 16-fold longer life than that of the adsorption column. Herein, we discovered and reported oxygen vacancies in silicon oxycarbide containing granular palm shell activated carbon (Si-PSAC) as a photocatalyst under UV irradiation. A strong correlation between the atomic content of Si1+, oxygen vacancies and photocatalytic performance of Si-PSAC was obtained. Based on the electron paramagnetic resonance and photoluminescence analyses, Si-PSAC under UVA 365 irradiation exhibited a higher donor density, better charge transfer and lower electron-hole recombination than that under the other light sources, leading to a higher O 2 · production efficiency. Si-PSAC exhibited effective removal performance for various anionic dyes and endocrine-disrupting chemicals under UVA 365 irradiation. Continuous-flow column tests revealed the life span of Si-PSAC under UVA 365 irradiation was extended by more than 16-fold compared to adsorption column. Since the oxygen vacancies can be created from the naturally present Si in the biomass derived Si-PSAC during the activation, this unexpected discovery of O 2 · production can extend commercially-available Si-PSAC into the full-scale photocatalysis. Image, graphical abstract [ABSTRACT FROM AUTHOR]