In this study, we report efficient gas–solid phase photocatalytic reaction by employing controlled periodic illumination, intense pulsed light (IPL) technique, at extremely low duty cycles. Compared with traditional continuous illumination, IPL exhibits superior photocatalytic performance, excellent economic advantages and extremely low duty cycles. Up to now, it is the first time that IPL has been applied in gas–solid phase photocatalytic reactions coupled with multiple photocatalysts. It is demonstrated by experiments that the pulsed xenon lamps can release a large number of photons in short pulsed time, leading to a much stronger photocurrent response than that triggered by a conventional xenon lamp. Taking photocatalytic benzenes degradation as the target reaction, in-situ EPR confirmed that the IPL system can generate a large number of reactive radicals, and thus can degrade benzenes efficiently even with almost negligible illumination period.
This study examined the role of intermittent illumination/dark conditions coupled with MnO 2 -ammendments to regulate the mobility of As and Fe in flooded arsenic-enriched soils. Addition of MnO 2 particles with intermittent illumination led to a pronounced increase in the reductive-dissolution of Fe(III) and As(V) from flooded soils compared to a corresponding dark treatments. A higher MnO 2 dosage (0.10 vs 0.02 g) demonstrated a greater effect. Over a 49-day incubation, maximum Fe concentrations mobilized from the flooded soils amended with 0.10 and 0.02 g MnO 2 particles were 2.39 and 1.85-fold higher than for non-amended soils under dark conditions. The corresponding maximum amounts of mobilized As were at least 92 % and 65 % higher than for non-amended soils under dark conditions, respectively. Scavenging of excited holes by soil humic/fulvic compounds increased mineral photoelectron production and boosted Fe(III)/As(V) reduction in MnO 2 -amended, illuminated soils. Additionally, MnO 2 amendments shifted soil microbial community structure by enriching metal-reducing bacteria (e.g., Anaeromyxobacter , Bacillus and Geobacter ) and increasing c -type cytochrome production. This microbial diversity response to MnO 2 amendment facilitated direct contact extracellular electron transfer processes, which further enhanced Fe/As reduction. Subsequently, the mobility of released Fe(II) and As(III) was partially attenuated by adsorption, oxidation, complexation and/or coprecipitation on active sites generated on MnO 2 surfaces during MnO 2 dissolution. These results illustrated the impact of a semiconducting MnO 2 mineral in regulating the biogeochemical cycles of As/Fe in soil and demonstrated the potential for MnO 2 -based bioremediation strategies for arsenic-polluted soils.
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