Toc 5 wp

The pH-value was determined at a soil to water ratio of 1:5 (wt/vol). Total nitrogen (TN) was determined using a modified Kjeldahl method. Ammonium ( ${\text{NH}}_4^{+}$ –N) and nitrate ( ${\text{NO}}_3^{-}$ –N) were measured using a continuous flow analyzer (Skalar SA 1000, Breda, The Netherlands). The soil samples for analysis of the dissolved organic carbon (DOC) were prepared by mixture with 0.5 M K₂SO₄ in a centrifuge tube, then shaking for 1 h on a reciprocal shaker and centrifuging at 13,000 rpm for 30 min at 4°C. The supernatant was filtered through a 0.45-μm glass fiber filter. All the extracts were analyzed by a continuous flow analyzer of San++ (Skalar SA 1000, Breda, The Netherlands).
Soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) were determined by the chloroform fumigation extraction method after 14 days of conditioning at 50% of their total water holding capacity under 25°C. This was followed by a 0.5 M K₂SO₄ extraction method for both the non-fumigated and fumigated samples (Brookes et al., 1985 (link); Vance et al., 1987 (link)). The SMBC extraction was analyzed by a TOC-V WP (SHIMADZU, Japan) and the SMBN extraction was digested and then analyzed by a San++ continuous flow analyzer (Skalar SA 1000, Breda, The Netherlands).

The concentration of RhB solution was 10 mg/L, and the dosage of manganese oxides is 0.5 g/L. The solution pH was adjusted to set value by HCl and NaOH. The mixture was allowed to react in room temperature with continuous stirring. At given time intervals, an appropriate amount of suspension was taken out and quickly diluted the density to the point with distilled water. For optical absorption measurements, the diluted solution was immediately centrifuged at 12,000 rpm for 10 min to remove the manganese oxide particles. The changes of absorptions at 554 nm were applied to identify the concentrations of RhB, using a Shimadzu UV-2450 UV–vis spectrophotometer. The released of Mn(II) in the solutions were analyzed by AAS.
RhB and the intermediates generated in the degradation process were analyzed with ultra performance liquid chromatography (UPLC) triple quadrupole mass spectrometry (TQMS). Chromatographic separation was performed on a Waters Acquity UPLC system with a Crestpak C18S column that was placed at 40°C. The mobile phase was methanol/ultra pure water (1:1, v/v) at a flow rate of 0.5 mL/min. The sample injection volume was 10 μL. Mass spectrometry analysis was conducted on a Waters Aquity TQ Detector with electro spray ionization (ESI). The total organic carbon concentration in solution was analyzed using TOC analyzer (Shimadzu, TOC-vwp).

The soil MBC analyses were conducted by chloroform fumigation-K₂SO₄ extraction carbon automatic analysis (Wu et al., 1990 (link)). Total organic C was extracted with K₂SO₄ (10 g of soil in 40 mL of 0.5 mol.L^-1 K₂SO₄) under fumigated and unfumigated status. Fumigated and unfumigated extracts were analyzed for total extractable organic C using a total organic carbon analyzer (Shimadzu TOC-Vwp; Shimadzu Corporation, Kyoto, Japan).