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 .

Nitrate Capture Investigation in Plasma-Activated Water and Its Antifungal Effect on Cryptococcus pseudolongus Cells.

This research investigated the capture of nitrate by magnesium ions in plasma-activated water (PAW) and its antifungal effect on the cell viability of the newly emerged mushroom pathogen Cryptococcus pseudolongus. Optical emission spectra of the plasma jet exhibited several emission bands attributable to plasma-generated reactive oxygen and nitrogen species. The plasma was injected directly into deionized water (DW) with and without an immersed magnesium block. Plasma treatment of DW produced acidic PAW. However, plasma-activated magnesium water (PA-Mg-W) tended to be neutralized due to the reduction in plasma-generated hydrogen ions by electrons released from the zero-valent magnesium. Optical absorption and Raman spectra confirmed that nitrate ions were the dominant reactive species in the PAW and PA-Mg-W. Nitrate had a concentration-dependent antifungal effect on the tested fungal cells. We observed that the free nitrate content could be controlled to be lower in the PA-Mg-W than in the PAW due to the formation of nitrate salts by the magnesium ions. Although both the PAW and PA-Mg-W had antifungal effects on C. pseudolongus, their effectiveness differed, with cell viability higher in the PA-Mg-W than in the PAW. This study demonstrates that the antifungal effect of PAW could be manipulated using nitrate capture. The wide use of plasma therapy for problematic fungus control is challenging because fungi have rigid cell wall structures in different fungal groups.

Removal of lead and bisphenol A using magnesium silicate impregnated palm-shell waste powdered activated carbon: Comparative studies on single and binary pollutant adsorption.

In this work, palm shell waste powder activated carbon coated by magnesium silicate (PPAC-MS) were synthesized by the impregnation of magnesium silicate (MgSiO3) using economical material (silicon dioxide powder) via mild hydrothermal approach for the first time. As an effective adsorbent, PPAC-MS simultaneously removes BPA and Pb(II) in single and binary mode. Surprisingly, PPAC-MS exhibited a homogeneous thin plate mesh-like structure, as well as meso- and macropores with a high surface area of 772.1m2g-1. Due to its specific morphological characteristics, PPAC-MS had adsorption capacities of Pb(II) as high as 419.9mgg-1 and 408.8mgg-1 in single mode and binary mode based on Freudliuch isotherm model while those for BPA by PPAC-MS were 168.4mgg-1 and 254.7mgg-1 for single mode and binary modes corresponding to Langmuir isotherm model. Experiment results also indicated that the synergistic removal of BPA occurred because the precipitation process of Pb(II) leads to the co-precipitation of BPA with Pb(OH)2 compound. PPAC-MS showed a good reusability for 5 regeneration cycles using Mg(II) solution followed by thermal treatment. Overall, PPAC-MS has a high potential in the treatment process for wastewater containing both toxic heavy metals and emerging pollutants due to its high sorption capacities and reusability.

New strategy to optimize in-situ Fenton oxidation for TPH contaminated soil remediation via artificial neural network approach.

In-situ remediation of total petroleum hydrocarbon (TPH) contaminated soils via Fenton oxidation is a promising approach. However, determining the proper injection amount of H2O2 and Fe source over the Fenton reaction in the complex geological conditions for in-situ TPH soil remediation remains a daunting challenge. Herein, we introduced a practical and novel approach using soft computational models, a multilayer perception artificial neural network (MPLNN), for predicting the TPH removal performance. In this study, we conducted 48 sets of TPH removal experiments using Fenton oxidation to determine the TPH removal performance of a wide range of different ground conditions and generated 336 data points. As a result, a negative Pearson correlation coefficient was obtained in the Fe injection mass and the natural presence of Fe mineral in the soil, indicating that the excess of Fe could significantly retarded the TPH removal performance in the Fenton reaction. In addition, the MPLNN model with 6-6-1 training using Scaled conjugate gradient backpropagation (SCG) with tangent sigmoid as the transfer function demonstrated a high accuracy for TPH removal prediction with the correlation determination of 0.974 and mean square error value of 0.0259. The optimized MPLNN model achieved less than 20% error for predicting TPH removal performance in actual TPH-contaminated soil via Fenton oxidation. Hence, the proposed MPLNN can be useful in improving the Fenton oxidation of TPH removal performance in-situ soil remediation.

Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review.

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

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.

Hydrophilic sulfurized nanoscale zero-valent iron for enhancing in situ biocatalytic denitrification: Mechanisms and long-term column studies.

The aim of this study was to investigate the effects of hydrophilic sulfur-modified nanoscale zero-valent iron (S-nZVI) as a biocatalyst for denitrification. We found that the denitrifying bacteria Cupriavidus necator (C. necator) promoted Fe corrosion during biocatalytic denitrification, reducing surface passivation and sulfur species leaching from S-nZVI. As a result, S-nZVI exhibited a higher synergistic factor (fsyn = 2.43) for biocatalytic NO3- removal than nanoscale zero-valent iron (nZVI, fsyn = 0.65) at an initial nitrate concentration of 25 mg L-1-N. Based on kinetic profiles, SO42- was the preferred electron acceptor over NO3- when using C. necator and S-nZVI for biocatalytic denitrification. Up-flow column experiments demonstrated that biocatalytic denitrification using S-nZVI achieved a total nitrogen removal capacity of up to 2004 mg L-1 for 127 d. Notably, microbiome taxonomic profiling showed that the addition of S-nZVI to the groundwater promoted the growth of Geobacter, Desulfosporosinus, Streptomyces, and Simplicispira spp in the column experiments. Most of those microbes can reduce sulfate, promote denitrification, and match the batch kinetic profile obtained using C. necator. Our results not only discover the great potential of S-nZVI as a biocatalyst for enhancing denitrification via microbial activation but also provide a deep understanding of the complicated abiotic-biotic interaction.

Insight into the role of charge carrier mediation zone for singlet oxygen production over rod-shape graphitic carbon nitride: Batch and continuous-flow reactor.

As a new approach of creating the photo-exited electron (e-) and hole (h+) mediation zone for highly selective singlet oxygen (1O2) production, the rod-type graphitic carbon nitride (NCN) has been synthesized from the nitric acid-modified melamine followed by the calcination. The NCN exhibited a higher surface area and surface oxygen adsorption ability than bulk graphitic carbon nitride (BCN). The increment of CO and NHx groups on NCN corresponded to e- and h+ mediation groups, respectively, resulting in higher production of 1O2 than BCN. Moreover, those mediation groups on NCN result in higher recombination efficiency and longer e- decay time. As a result, the optimized NCN-0.5 (derived from 0.5 M of nitric acid-modified melamine) displayed 5.8 times higher kinetic rate constant of atrazine (ATZ) removal under UVA-LED irradiation compared to BCN. This study also evaluated the ATZ degradation pathways and toxicity effect of by-products. In addition, continuous flow experiments using NCN-0.5 showed superior ATZ removal performance with a hybrid concept between a slurry photocatalysis and a continuous stirred tank reactor system using actual effluent obtained from a wastewater treatment plant. Thus, this work provides an insight into the strategy for highly selective 1O2 production and the potential for water purification application.

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.

Catalytic non-thermal plasma treatment of endocrine disrupting compounds, pharmaceuticals, and personal care products in aqueous solution: A review.

Contaminants of emerging concerns such as endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal-care products (PPCPs) constitute a problem since they are not completely eliminated by traditional water and wastewater treatment methods. Non-thermal plasma (NTP) is considered as one of the most favorable treatment methods for the removal of organic contaminants in water and wastewater. The degradation of selected EDCs and PPCPs of various classes was reviewed, based on the recent literature, to (i) address the effect of the main NTP treatment parameters (water quality and NTP conditions: pH, initial concentration, temperature, background common ion, NOM, scavenger, gas type/flow rate, discharge/reactor type, input power, and energy efficiency/yield) on the degradation of contaminants and their intermediates, (ii) assess the influences of different catalysts and hybrid systems on degradation, (iii) describe EDC and PPCP degradation along with their properties, and (iv) evaluate mineralization, pathway, and degradation mechanism of selected EDCs and PPCPs for different cases studied. Furthermore, areas of potential research in NTP treatment for the degradation of EDCs and PPCPs in aqueous solutions are recommended. It could be reasonably predicted that this review is valid for developing our understanding of the fundamental scientific principles concerning the catalytic NTP of EDCs and PPCPs, providing helpful and practical references for researchers and designers on the effective removal of EDCs/PPCPs and the optimized operation of catalytic NTP systems.

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.

Degradation synergism between sonolysis and photocatalysis for organic pollutants with different hydrophobicity: A perspective of mechanism and application for high mineralization efficiency.

Despite extensive studies, the fundamental understanding of synergistic mechanisms between sonolysis and photocatalysis for the abatement of persistent organic pollutants (POPs) remains uncertain. As different phases formed under ultrasound irradiation, hydrophilic POPs, sulfamethoxazole (SMX, Kow: 0.89), predominantly resides in bulk liquid and is ineffectively degraded by sonolysis (kUS = 3.33 × 10-3 min-1) since <10% of hydroxyl radicals (·OH) formed at the gas-liquid interface of cavitation is diffused into the bulk, whereas the other fraction rapidly recombines into hydrogen peroxide (H2O2). This study provides a proof-of-concept for the mechanism by presenting various analytical results, endorsing the synergistic role of photoexcited electrons in splitting sonolysis-induced H2O2 into ·OH, particularly in the bulk phase. In a sonophotocatalytic system, the hydrophobic POPs such as bisphenol A (BPA) and atrazine (ATZ) were mainly degraded in gas-liquid interface indicated by the low synergistic values correlation compared to SMX [i.e., SMX has a higher synergistic factor, fsyn (3.26) than BPA (1.30) and ATZ (1.35)]. Also, fsyn was found linearly correlated with the contribution factor of photocatalysis to split H2O2. Three times of consecutive kinetics using an effluent of municipal (MP) wastewater spiked by POPs presented >98% POPs and >96% total organic carbon (TOC) removal.

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.

Mechanism of simultaneous removal of aluminum and fluoride from aqueous solution by La/Mg/Si-activated carbon.

La/Mg/Si-activated carbon derived from palm shell has been a suitable material for removal of aluminum and fluoride from aqueous solution. In the study, the mechanism of simultaneous removal of aluminum and fluoride by La/Mg/Si-activated carbon (La/Mg/Si-AC) was investigated to understand its high efficiency. It was found that the removal of aluminum and fluoride by La/Mg/Si-AC was favored at lower pH compared to the point of zero charge of La/Mg/Si-AC and high temperature. Adsorption capacity of Al(OH)4- was about 10 times higher than that of F- due to the strong binding affinity of Al(OH)4- on protonated surface and competition between F- and OH- toward charged adsorption site. Kinetics results showed that the aluminum and fluoride adsorption were explained using the pseudo-second-order kinetic model and intra-particle diffusion model. Adsorption process of Al(OH)4- and F- was driven by the potential rate-limiting step involved in mass transport process occurred on the boundary diffusion layer of porous adsorbent surface. Electrostatic interaction between protonated surface of La/Mg/Si-AC and negatively charged ions (i.e., Al(OH)4- and F-) as well as ion-exchange between hydroxide and ionic metal species were important mechanisms in the process of aluminum and fluoride adsorption. Driving forces for adsorption of individual Al(OH)4- and F- were not entirely different. Identifying the dominant mechanism will be helpful in understanding the adsorption process and developing new adsorbent.

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.

Mesoporous silica from batik sludge impregnated with aluminum hydroxide for the removal of bisphenol A and ibuprofen.

The present study reports the removal of Bisphenol A (BPA) and Ibuprofen (IBP) using adsorbents prepared from batik sludge. The calcite sludge-aluminum hydroxide (CAl) adsorbent was prepared by calcination and followed by aluminum hydroxide impregnation. The batik sludge and prepared adsorbents were characterized by FESEM, TGA, XRD, FTIR and BET techniques. The maximum adsorption capacity, adsorption time, different initial solution pH, ionic strength and regeneration study of the adsorbents were also investigated. Furthermore, the sorption behavior of the pollutants were studied by the Langmuir and Freundlich isotherms. The deposition of Al(OH)3 enhanced the BPA and IBP adsorption capacity on the CAl surface. The maximum removal capacity of BPA and Ibuprofen were 83.53 mg g-1 and 34.96 mg g-1 for the CAl adsorbent. In addition, the kinetic data for BPA and IBP were fitted to the pseudo first order, pseudo second order, Elovich, parabolic diffusion and power function equations to understand the sorption behavior. The adsorption behavior of BPA and IBP was mainly chemisorption. This study shows that CAl is a promising adsorbent for the removal of BPA and IBP.