Alendronate-Functionalized Graphene Quantum Dots as an Effective Fluorescent Sensing Platform for Arsenic Ion Detection

Alendronate-functionalized graphene quantum dots (ALEN-GQDs) with a quantum yield of 57% were synthesized via a two-step route: preparation of graphene quantum dots (GQDs) by pyrolysis method using citric acid as the carbon source and post functionalization of GQDs via a hydrothermal method with alendronate sodium. After careful characterization of the obtained ALEN-GQDs, they were successfully employed as sensing materials with superior selectivity and sensitivity for the detection of nanomolar levels of arsenic ions (As(III)). According to the mechanistic investigation, arsenic ions can quench the fluorescence intensity of ALEN-GQDs through metal-ligand interaction between the As(III) ions and the surface functional groups of the fluorescent probe. This probe provided a rapid method to monitor As(III) with a wide detection range (44 nM-1.30 µM) and a low detection limit of 13 nM. Finally, to validate the applicability, this novel fluorescent probe was successfully applied for the quantitative determination of As(III) in rice and water samples.

Adsorption of arsenic in aqueous solution onto iron impregnated bagasse fly ash

The present study examined the adsorption of As(III) and As(V) (arsenics) from aqueous solutions using FeCl3 impregnated bagasse fly ash (BFA-Fe). Batch adsorption studies were carried out to evaluate the effect of various parameters like initial pH (pH 0 ), adsorbent dose (m), contact time (t), initial concentration (C 0 ) and temperature (T) on the removal of As(III) and As(V) from aqueous solutions. The maximum removal of As(III) and As(V) was found ~ 95% and ~ 97% at lower concentration (< 20 μg/dm3) and ~ 86% and ~ 87% at higher concentration (500 μg/dm3), respectively, using 3 g/dm3 of BFA dosage at 303 K. The adsorption of arsenics on BFA-Fe was very rapid. Pseudo-second-order kinetic model well represented the adsorption kinetics of both As(III) and As(V). Error analyses functions for adsorption of As(III) and As(V) onto BFA-Fe. Based on these error analyses, R-P isotherm was found to be fitted. Thermodynamic parameters, i.e., ΔG°, ΔH°, and ΔS°, were also calculated. At 25.0 to 45.0 °C, the values of ΔG° lie in the range of -43.85, -45.34, -48.82, -51.31, -53.8, and -44.75, -48.3, -51.84, -55.39, -58.93, -55.57 for As (III), and As (V) respectively, indicating that adsorption is spontaneous and exothermic in nature. Regeneration study was carried out by different solvent and thermal methods. Our results revealed that BFA-Fe can be reused directly for making fire-briquettes to explore its energy value. From this study, As containment is most effective removal from aqueous solution and mimic to any contaminated water resources.

Surface protection method for the magnetic core using covalent organic framework shells and its application in As(III) depth removal from acid wastewater

Fe₃O₄-based materials are widely used for magnetic separation from wastewater. However, they often suffer from Fe-leaching behavior under acidic conditions, decreasing their activity and limiting sustainable practical applications. In this study, covalent organic frameworks (COFs) were used as the shell to protect the Fe₃O₄ core, and the Fe₃O₄@COF core-shell composites were synthesized for As(III) removal from acid wastewater. The imine-linked COFs can in situ grow on the surface of the Fe₃O₄ core layer by layer with [COFs/Fe₃O₄]_mol ratio of up to 2:1. The Fe-leaching behavior was weakened over a wide pH range of 1-13. Moreover, such composites keep their magnetic characteristic, making them favorable for nanomaterial separation. As(III) batch adsorption experiments results indicated that, when COFs are used as the shell for the Fe₃O₄ core, a balance between As(III) removal efficiencies and the thickness of the COF shell exists. Higher As(III) removal efficiencies are obtained when the [COFs/Fe₃O₄]_mol ratios were < 1.5:1, but thicker COF shells were not beneficial for As(III) removal. Such composites also exhibited better As(III) removal performances in the pH range of 1-7. Over a wide pH range, the zeta potential of Fe₃O₄@COF core-shell composites becomes more positive, which benefits the capture of negative arsenic ions. In addition, thinner surface COFs were favorable for mass transfer and facilitating the reaction of Fe and As elements. Our study highlights the promise of using COFs in nanomaterial surface protection and achieving As(III) depth removal under acidic conditions.

The differential inhibitive effects and fates of As(III) and As(V) mediated by Sulfobacillus thermosulfidooxidans grown on S0, Fe2+ and FeS2

Arsenic often coexists with metal sulfide minerals and occurs in different speciation and different toxicity in responding to Fe/S biooxidation. The differential inhibitive effects and fates of As(III) and As(V) during biooxidations of elemental sulfur (S⁰), ferrous ions (Fe²⁺) and pyrite (FeS₂) by Sulfobacillus thermosulfidooxidans were studied. The results revealed that the arsenic species hardly changed for the biooxidation of S⁰, but dramatically changed for the biooxidation of Fe²⁺ and FeS₂. Different transformation degree between As(III) and As(V) occurred for biooxidation of FeS₂ in the presence of arsenic, where about 72% of As(III) was transformed to As(V) for the group with As(III) added, and 16% of As(V) was transformed to As(III) for that with As(V) added. Both formation and dissolution of amorphous ferric arsenate occurred during biooxidation of FeS₂ with the addition of As(III) or As(V) and for the group grown on Fe²⁺ with added As(V), which were controlled by the changes of Fe/As molar ratio and pH value in the solution. Jarosite was detected for the group grown on Fe²⁺ and could adsorb As(III) and As(V). The inhibitive effects of As(V) were higher than As(III) when the strain grew on FeS₂, which was contrary to those when the strain grew on S⁰ and Fe²⁺. The above results signify that the fates and inhibitive effects of arsenic are much related to each other, and such a relationship is significantly affected by the utilization of Fe/S energy substrates by the sulfur- and ferrous-oxidizing microorganisms.