Highly Exposed NH2 Edge on Fragmented g-C3 N4 Framework with Integrated Molybdenum Atoms for Catalytic CO2 Cycloaddition: DFT and Techno-Economic Assessment.

This study focuses on the applicability of single-atom Mo-doped graphitic carbon nitride (GCN) nanosheets which are specifically engineered with high surface area (exfoliated GCN), NH2 rich edges, and maximum utilization of isolated atomic Mo for propylene carbonate (PC) production through CO2 cycloaddition of propylene oxide (PO). Various operational parameters are optimized, for example, temperature (130 °C), pressure (20 bar), catalyst (Mo2 GCN), and catalyst mass (0.1 g). Under optimal conditions, 2% Mo-doped GCN (Mo2 GCN) has the highest catalytic performance, especially the turnover frequency (TOF) obtained, 36.4 h-1 is higher than most reported studies. DFT simulations prove the catalytic performance of Mo2 GCN significantly decreases the activation energy barrier for PO ring-opening from 50-60 to 4.903 kcal mol-1 . Coexistence of Lewis acid/base group improves the CO2 cycloaddition performance by the formation of coordination bond between electron-deficient Mo atom with O atom of PO, while NH2 surface group disrupts the stability of CO2 bond by donating electrons into its low-level empty orbital. Steady-state process simulation of the industrial-scale consumes 4.4 ton h-1 of CO2 with PC production of 10.2 ton h-1 . Techno-economic assessment profit from Mo2 GCN is estimated to be 60.39 million USD year-1 at a catalyst loss rate of 0.01 wt% h-1 .

Organic pollutants degradation using plasma with simultaneous ammonification assisted by electrolytic two-cell system.

Atmospheric non-thermal dielectric barrier discharge (DBD) plasma has gained considerable attention due to its cost-efficiency, environmental friendliness, and simplicity. However, certain deficiencies restrict its broad application. Herein, the DBD plasma was used to disrupt three model pharmaceutically active compounds (PhACs), sulfamethoxazole (SMX), ibuprofen (IBP), and norfloxacin (NFX), by varying parameters, such as gas type (Ar, N2, O2, and air) and flow rate (1-4 L min-1). The air plasma discharge had the highest degradation efficiency, and the air flow rate was optimized at 2 L min-1. However, only 10% of IBP was removed by the sole plasma, whereas NFX and SMX were entirely removed after 30 min. Since the air plasma discharge generates reactive oxygen and nitrogen species in a chained reaction, the remaining NO2- and NO3- in the aqueous phase were problematic. Therefore, by coupling plasma with electrolysis using Cu/reduced Cu nanowire (R-CuNw) as the anode/cathode, all three PhACs were removed within 30 min, and NO2- and NO3- were completely reduced to NH3 with cathodic reduction. Moreover, the electrical energy per order (EEO, 0.04 kWh L-1) and treatment cost (0.003 USD L-1) were much lower than those of the single system. This system demonstrates great potential for water remediation, and the production of NH3 as a value-added by-product remarkably improves its practicality and is of great importance in agriculture and energy-related industries.

In-situ growth of manganese oxide on self-assembled 3D- magnesium hydroxide coated on polyurethane: Catalytic oxidation mechanism and application for Mn(II) removal.

Novel integration of adsorption followed by catalytic oxidation is expected to be more beneficial for higher Mn(II) removal performance. We prepared self-assembled 3D flower-like Mg(OH)2 coated on granular-sized polyurethane (namely FMHP) via hydrothermal method at 120 °C under a facile synthesis route. The optimized material, FMHP prepared with 7 g MgO and 20 g polyurethane (FMH0.35P), achieved up to 351.2 mg g-1 Mn(II) removal capacity by Langmuir isotherm model. Besides, FMHP exhibited high Mn(II) removal in a wide range of NaCl concentration (0~0.1 M) and pH 2-9. Notably, through consecutive kinetics, BET, XPS, XRD, FESEM, and TEM analyses, it was found that the MnOx layer grows in-situ via ion exchange with Mg(II) on FMHP and further boosts the Mn(II) removal via catalytic oxidation during the Mn(II) removal process. Further, column experiments revealed that the FMH0.35P exhibited superior Mn(II) removal capacities up to 135.9 mg g-1 and highly compatible treatment costs ($0.062 m-3) compared to conventional chemical processes. The granular-sized FMH0.35P prepared by economic precursors and simple synthesis route revealed a high potential for Mn(II) containing water treatment due to its high removal capacities and easy operation.

In situ Fenton remediation for diesel contaminated clayey zone assisted by thermal plasma blasting: Synergism and cost estimation.

Thermal plasma blasting technology has been widely applied for rock cracking. Though, the application for environmental remediation has yet to be reported. Since the delivery of remediation agents into diesel contaminated clayey zones are exceptionally challenging, herein, this study explores the effect of pilot-scale thermal plasma blasting for soil fracturing and concurrently dispersing the Fenton reagent into the diesel contaminated silty soils. Six times plasma blasting with sole H2O2 at 20 kV had the highest degradation of diesel (>97%) with an equilibrium time of 3 h, and the final diesel concentration was below the South Korean regulated health standard (500 mg kg-1). This study highlights plasma blasting able to deliver H2O2 instantaneously and homogeneously into contaminated zone while promoting Fenton reaction synergism (fsyn: 2.04) between H2O2 and ≡Fe surface for effective remediation. Furthermore, the remediation cost (USD 4 metric ton-1) is much lower than most reported in situ technologies.

Sulfur-anchored palm shell waste-based activated carbon for ultrahigh sorption of Hg(II) for in-situ groundwater treatment.

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 Na2S > Na2S2O4 > CH3CSNH2 sequence. PSAC-S prepared using Na2S 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 HgSO4. 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.

Unexpected discovery of superoxide radical generation by oxygen vacancies containing biomass derived granular activated carbon.

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 UVA365 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 O2· production efficiency. Si-PSAC exhibited effective removal performance for various anionic dyes and endocrine-disrupting chemicals under UVA365 irradiation. Continuous-flow column tests revealed the life span of Si-PSAC under UVA365 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 O2· production can extend commercially-available Si-PSAC into the full-scale photocatalysis.

Granular Mg-Fe layered double hydroxide prepared using dual polymers: Insights into synergistic removal of As(III) and As(V).

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 (PAM40/PVA30-LDH) and restructured the crystal phase from monoclinic to orthorhombic. This increased the surface area and pore volume. Furthermore, PAM40/PVA30-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 PAM40/PVA30-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 PAM40/PVA30-LDH was mainly attributable to ion exchange with intercalated SO42-, hydrogen bonding, and complexation mechanisms. These findings illustrate that PAM40/PVA30-LDH would be an excellent adsorbent for the remediation of arsenic-polluted wastewater.

Fluoride removal by palm shell waste based powdered activated carbon vs. functionalized carbon with magnesium silicate: Implications for their application in water treatment.

In this study, palm shell activated carbon powder (PSAC) and magnesium silicate (MgSiO3) 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 MgSiO3 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.