Titanium Dioxide Nanoparticles Induced an Enhanced and Intimately Coupled Photoelectrochemical-Microbial Reductive Dissolution of As(V) and Fe(III) in Flooded Arsenic-Enriched Soils

Abstract

Nanosized titanium dioxide (TiO2) is a naturally existing nanoscale semiconducting mineral, and its co-occurrence with microbes may elicit differential environmental effects. In this study, the impacts of TiO2 nanoparticles (NPs) on the reductive dissolution of As­(V) and Fe­(III) from flooded arsenic-enriched soils were examined under intermittent illumination and dark conditions. The amendment with TiO2 NPs under intermittent illumination resulted in the highest As/Fe reduction among all amendments. In the amendment with TiO2 NPs, the maximum concentrations of Fe­(II) derived from intermittent illumination and dark treatments were nearly 2.1- and 1.7-fold higher than the soils amended with acetate alone under dark conditions (36.5 ± 4.5 mg/L), respectively, and nearly 1.6- and 1.2-fold higher than the increased As­(III) concentrations (8175.2 ± 125.5 μg/L) detected under the same conditions. However, the removal of total organic carbon derived from the amendment with acetate-TiO2 NPs under intermittent illumination was only 0.8 times that of the amendment with acetate alone under dark conditions. Because TiO2 NPs are highly responsive to sunlight, more photoelectrons supplied from intermittently illuminated soils were separated synchronously by accompanying them with the capture of photoholes by humic/fulvic acids; thereafter, the photoelectrons participated in As­(V)/Fe­(III) reduction. In addition, the electrical conductivities of TiO2 NPs-supplemented soil particles were nearly 1.6-fold higher than that of nonsupplemented samples, thereby enabling a long-distance electron transfer. Moreover, the amendment with TiO2 NPs with intermittent illumination resulted in an increase to the abundances of several metal-reducing bacteria in the soil microbial community, e.g., Bacillus, Thermincola, Pseudomonas, and Clostridium, correspondingly boosting the involved microbial degradation of organic substrates to supply more bioelectrons for As­(V)/Fe­(III) reduction. The findings have an important implication on the understanding of the role of nanosized minerals in the biogeochemical cycling of metal pollutants.

Role of MnO2 in controlling iron and arsenic mobilization from illuminated flooded arsenic-enriched soils

“…Importantly, Fe(III) dissolution was promoted by intermittent illumination compared to dark conditions. We attributed this response to enhanced production of photoelectrons originating from the illuminated endogenous minerals that then flowed into microbial extracellular electron transfer chains (Chen et al, 2019b). MnO 2 -ammended soils showed a sharp decrease in reductive dissolution of Fe(III) and demonstrated a dose-dependent response.…”

“…2). Thus, we inferred that a greater amount of photoelectrons excited from exogenous semiconducting MnO 2 particles were supplied to promote the higher reductive dissolution of As(V)/Fe(III) in the intermittently illuminated assays (Chen et al, 2019b). Additional evidence for this supposition resulted from a greater decline of fluorescence signals, corresponding to the heavy-molecular-weight humic/ fulvic acids-like compounds, in the intermittent illumination versus dark treatments (Fig.…”

Biophotoelectrochemistry for renewable energy and environmental applications

“…The study on the natural BPEC systems at the water-sediment interface is at a very early stage and mainly focuses on the metal elements. It was reported that the photo-excited mineral photoelectrons from various SQDs such as ZnS, MnO 2 and TiO 2 , participated in the microbial electron transfer chain for As/Fe reduction in flooded soils, and the synchronously excited photoholes could be scavenged by humic/fulvic acids (Dong et al, 2021;Chen et al, 2019cChen et al, , 2019d. The introduction of these SQDs would increase the electrical conductivities of soil particles and enhance the production of c-type cytochrome, thereby enabling a long-distance photoelectron transfer.…”

“…This phenomenon is widely discovered in both natural and artificial environments. The former can occur in mineral coating (Lu et al, 2012), flooded soils (Chen et al, 2019c(Chen et al, , 2019d, and offshore areas (Liu et al, 2020) for the specific biogeochemical redox processes due to the widespread existence of electrotrophs (e.g., Acidithiobacillus ferrooxidans, Alcaligenes faecalis, S. oneidensis and Geobacter metallireducens) and natural semiconductor minerals (e.g., rutile [TiO 2 ], sphalerite [ZnS], and goethite [FeOOH]). The latter holds a great potential for pollutant control and energy production in engineered systems like biological wastewater treatment.…”

Recent advances in the roles of minerals for enhanced microbial extracellular electron transfer

“…illumination [118,119]. Notably, there was improved bacterial viability in biofilms and high enrichment of Geobacteraceae (a nearly 1.5-fold increase of relative abundance vs. control) in a photobioanode that was equipped with hematite [120].…”