Adsorption-coupled Fenton type reduction of bromate in water by high-yield polymer-derived ceramic-supported nano-zerovalent iron.

Nano-zerovalent iron (nZVI) is a promising material for the removal of both organic and inorganic pollutants from contaminated water. This study investigates the potential of a novel composite of nZVI on a polymer-derived supporting ceramic (nZVI-PDC) synthesized via the liquid-phase reduction method for the simultaneous adsorption and Fenton-type reduction of bromate anion (BrO3-) in water. The nZVI nanoparticles were effectively anchored onto the PDC by impregnating high-yield carbon in a ferrous sulfate solution. The PDC facilitated the uniform dispersion of nZVI nanoparticles due to its multiple active sites distributed within mesocarbon cavities. The developed nZVI-PDC composite exhibited a high specific surface area of 837 m2 g-1 and an ordered mesoporous structure with a pore volume of 0.37 cm3 g-1. As an adsorbent, the nZVI-PDC composite exhibited a maximum adsorption capacity (qe) of 842 mg g-1 and a partition coefficient (KH) of 10.2 mg g-1 µM-1, as calculated by the pseudo-second-order model. As a catalyst, the composite demonstrated a reaction kinetic rate of 43.5 µmol g-1 h-1 within 6 h at pH 4, using a dosage of 60 mg L-1 nZVI-PDC and a concentration of 0.8 mmol L-1 H2O2. Comparatively, PDC exhibited a qe of 408 mg g-1, KH of 1.67 mg g-1 µM-1, and a reaction rate of 20.8 µmol g-1 h-1, while nZVI showed a qe of 456 mg g-1, KH of 2.30 mg g-1 µM-1, and a reaction rate of 27.2 µmol g-1 h-1. The modelling indicated that the nZVI-PDC composite followed pseudo-second-order kinetics. The remarkable removal efficiency of the nZVI-PDC composite was attributed to the synergistic effects between PDC and nZVI, where PDC facilitated charge transfer, promoting Fe2+ generation and the Fe3+/Fe2+ cycle. Overall, this work introduces a promising adsorption technology for the efficient removal of BrO3- from contaminated aqueous solutions, highlighting the significant potential of the nZVI-PDC composite in water purification applications.

Role of organic and inorganic amendments on physiological attributes of germinating pea seedlings under arsenic stress.

There are scarce data regarding the effects of soil amendments on biophysicochemical responses of plants at the early stages of growth/germination. This study critically compares the effects of ethylene-diamine-tetra-acetic-acid (EDTA) and calcium (Ca) on biophysicochemical responses of germinating pea seedlings under varied arsenic levels (As, 25, 125, 250 µM). Arsenic alone enhanced hydrogen peroxide (H2O2) level in pea roots (176%) and shoot (89%), which significantly reduced seed germination percentage, pigment contents, and growth parameters. Presence of EDTA and Ca in growth culture minimized the toxic effects of As on pea seedlings, EDTA being more pertinent than Ca. Both the amendments decreased H2O2 levels in pea tissues (16% in shoot and 13% in roots by EDTA, and 7% by Ca in shoot), and maintained seed germination, pigment contents, and growth parameters of peas close to those of the control treatment. The effects of all As-treatments were more pronounced in the pea roots than in the shoot. The presence of organic and inorganic amendments can play a useful role in alleviating As toxicity at the early stages of pea growth. The scarcity of data demands comparing plant biophysicochemical responses at different stages of plant growth (germinating vs mature) in future studies.

Till date, abundant research has focused on plant biophysicochemical responses to different types of pollutants. However, the majority of these studies dealt with pollutant exposure to mature plants (generally after a vegetative growth period of 1­2 weeks). Despite significant research, there are still limited data regarding the biophysicochemical responses of plants at their early stages of germination and growth. In fact, stresses at germination or at an early stage of growth can be highly fatal and may significantly affect the ultimate plant growth and potential to remediate the contaminated sites. Therefore, the current study deals with the exposure of germinating pea seedlings to arsenic (As) stress under varied amendments. This experimental plan helped to understand the initial biophysicochemical changes induced in pea plants under As stress.

Super capacity of ligand-engineered biochar for sorption of malachite green dye: key role of functional moieties and mesoporous structure.

This study synthesized a new thiomalic acid-modified rice husk biochar (TMA-BC) as a versatile and eco-friendly sorbent. After undergoing chemical treatments, the mercerized rice husk biochar (NaOH-BC) and TMA-BC samples showed higher BET surface area values of 277.1 m2/g and 305.8 m2/g, respectively, compared to the pristine biochar (BC) sample, which had a surface area of 234.2 m2/g. In batch adsorption experiments, it was found that the highest removal efficiency for malachite green (MG) was achieved with TMA-BC, reaching 96.4%, while NaOH-BC and BC exhibited removal efficiencies of 38.6% and 27.9%, respectively, at pH 8. The engineered TMA-BC exhibited a super adsorption capacity of 104.17 mg/g for MG dye at pH 8.0 and 25 °C with a dosage of 2 g/L. The SEM, TEM, XPS, and FTIR spectroscopy analyses were performed to examine mesoporous features and successful TMA-BC carboxylic and thiol functional groups grafting on biochar. Electrostatic forces, such as π - π interactions, hydrogen bonding, and pore intrusion, were identified as key factors in the sorption of MG dye. As compared to single-solution adsorption experiments, the binary solution experiments performed at optimized dosages of undesired ions, such as humic acid, sodium dodecyl sulfate surfactant, NaCl, and NaSCN, reflected an increase in MG dye removal of 2.8%, 8.7%, 5.4%, and 12.7%, respectively, which was attributed to unique mesoporous features and grafted functional groups of TMA-BC. Furthermore, the TMA-BC showed promising reusability up to three cycles. Our study indicates that mediocre biochar modified with TMA can provide an eco-friendly and cost-effective alternative to commercially accessible adsorbents.

Evaluation of iron-modified biochar on arsenic accumulation by rice: a pathway to assess human health risk from cooked rice.

Arsenic (As) contamination of rice grain poses a serious threat to human health. Therefore, it is crucial to reduce the bioavailability of As in the soil and its accumulation in rice grains to ensure the safety of food and human health. In this study, mango (Mangifera indica) leaf-derived biochars (MBC) were synthesized and modified with iron (Fe) to produce FeMBC. In this study, 0.5 and 1% (w/w) doses of MBC and FeMBC were used. The results showed that 1% FeMBC enhanced the percentage of filled grains/panicle and biomass yield by 17 and 27%, respectively, compared to the control. The application of 0.5 and 1% FeMBC significantly (p < 0.05) reduced bioavailable soil As concentration by 33 and 48%, respectively, in comparison to the control. The even higher As flux in the control group as compared to the biochar-treated groups indicates the lower As availability to biochar-treated rice plant. The concentration of As in rice grains was reduced by 6 and 31% in 1% MBC and 1% FeMBC, respectively, compared to the control. The reduction in As concentration in rice grain under 1% FeMBC was more pronounced due to reduced bioavailability of As and enhanced formation of Fe-plaque. This may restrict the entry of As through the rice plant. The concentrations of micronutrients (such as Fe, Zn, Se, and Mn) in brown rice were also improved after the application of both MBC and FeMBC in comparison to the control. This study indicates that the consumption of parboiled rice reduces the health risk associated with As compared to cooked sunned rice. It emphasizes that 1% MBC and 1% FeMBC have great potential to decrease the uptake of As in rice grains.

A critical review on the organo-metal(loid)s pollution in the environment: Distribution, remediation and risk assessment.

Toxic metal(loid)s, e.g., mercury, arsenic, lead, and cadmium are known for several environmental disturbances creating toxicity to humans if accumulated in high quantities. Although not discussed critically, the organo-forms of these inorganic metal(loid)s are considered a greater risk to humans than their elemental forms possibly due to physico-chemical modulation triggering redox alterations or by the involvement of biological metabolism. This extensive review describes the chemical and physical causes of organometals and organometal(loid)s distribution in the environment with ecotoxicity assessment and potential remediation strategies. Organo forms of various metal(loid)s, such as mercury (Hg), arsenic (As), lead (Pb), tin (Sn), antimony (Sb), selenium (Se), and cadmium (Cd) have been discussed in the context of their ecotoxicity. In addition, we elaborated on the transformation, speciation and transformation pathways of these toxic metal(loid)s in soil-water-plant-microbial systems. The present review has pointed out the status of toxic organometal(loid)s, which is required to make the scientific community aware of this pressing condition of organometal(loid)s distribution in the environment. The gradual disposal and piling of organometal(loid)s in the environment demand a thorough revision of the past-present status with possible remediation strategies prescribed as reflected in this review.

Enhanced capacity of thiol-functionalized sugarcane bagasse and rice husk biochars for arsenite sorption in aqueous solutions.

The utilization of biowastes for producing biochar to remove potentially toxic elements from water represents an important pathway for aquatic ecosystem decontamination. Here we explored the significance of thiol-functionalization on sugarcane bagasse biochar (Th/SCB-BC) and rice husk biochar (Th/RH-BC) to enhance arsenite (As(III)) removal capacity from water and compared their efficiency with both pristine biochars (SCB-BC and RH-BC). The maximum As(III) sorption was found on Th/SCB-BC and Th/RH-BC (2.88 and 2.51 mg g-1, respectively) compared to the SCB-BC and RH-BC (1.51 and 1.40 mg g-1). Relatively, a greater percentage of As(III) removal was obtained with Th/SCB-BC and Th/RH-BC (92% and 83%, respectively) at a pH 7 compared to pristine SCB-BC and RH-BC (65% and 55%) at 6 mg L-1 initial As(III) concentration, 2 h contact time and 1 g L-1 sorbent dose. Langmuir (R2 = 0.99) isotherm and pseudo-second-order kinetic (R2 = 0.99) models provided the best fits to As(III) sorption data. Desorption experiments indicated that the regeneration ability of biochars decreased and it was in the order of Th/SCB-BC (88%) > Th/RH-BC (82%) > SCB-BC (77%) > RH-BC (69%) up to three sorption-desorption cycles. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy results demonstrated that the thiol (-S-H) functional groups were successfully grafted on the surface of two biochars and as such contributed to enhance As(III) removal from water. Spectroscopic data indicated that the surface functional moieties, such as -S-H, - OH, - COOH, and C = O were involved to increase As(III) sorption on thiol-functionalized biochars. This study highlights that thiol-grafting on both biochars, notably on SCB-BC, enhanced their ability to remove As(III) from water, which can be used as an effective technique for the treatment of As from drinking water.