Highly efficient redox reaction between potassium permanganate and 3,3′,5,5′-tetramethylbenzidine for application in hydrogen peroxide based colorimetric assays

Ultrathin porous Pd metallene as highly efficient oxidase mimics for the colorimetric detection of chromium (VI)

Palladium (Pd)-based nanomaterials are the emerging class of catalysts with individual physiochemical properties. Unlike traditional catalysts, metallenes showed abundant active sites, large surface area, and high atomic utilization. Based on these benefits, we demonstrate a highly active 2D graphene-like Pd metallene with abundant accessible active sites serving as a highly efficient oxidase mimic. The structure and morphology of Pd metallenezymes were controlled to enhance the catalytic performance and to efficiently utilize all the Pd atoms. Pd metallenezymes with excellent oxidase-like activity were successfully applied for colorimetric-based chromium (VI) (Cr(VI)) detection in a real environment. 3,3',5,5'-Tetramethylbenzidine (TMB) was used as a typical chromogenic substrate catalyzed by Pd metallene to show that blue oxidized TMB (ox TMB) was significantly reduced to colorless TMB by the reducing agent 8-hydroxyquinoline (8-HQ). The reaction process was impressively reversed by the addition of Cr(VI), which interacted with 8-HQ to restore the blue color of TMB. Based on the above results, a facile and effective colorimetric sensing system for the detection of Cr(VI) with a low detection limit of 2.8 nM was developed and could be successfully applied to the detection of Cr(VI) in a real environment.

Heavy metal content and microbial characteristics of soil plant system in Dabaoshan mining area, Guangdong Province

The disordered mining of Dabaoshan lead-zinc mineral resources in Shaoguan has brought serious harm to the regional ecological environment. In order to investigate the heavy metal pollution status and microbial characteristics of soil plant system in mining area, The distribution of heavy metals in the soil, the activity of soil microorganisms and the accumulation characteristics of heavy metals in the dominant plant Miscanthus floridulus were studied. The results indicated that metal element contents of Miscanthus floridulus in sequence were: Zn>Pb>Cu> Cd. This study demonstrated that the elemental content of the Miscanthus floridulus plant showed Zn>Pb>Cu>Cd, with Zn being the most significantly correlated with soil elements, followed by Pb. Compared with the control group, the Miscanthus floridulus-soil system possessed obviously different soil microbial features: intensiver in microbial basal respiration strength, and higher microbial eco-physiological parameters Cmic/Corg and qCO2, but lower in soil microbial biomass. The results showed the soil enzymatic activities decreased significantly with increase of contamination of heavy metals, especially dehydrogenase and urease activities. With the increase of the content of heavy metals in the mining area soil, the intensity of soil biochemical action in the mining area (Q1, Q2) soil decreased significantly, and the biochemical action showed a significant negative correlation with the content of heavy metals in the soil. Compared with the non mining area (Q8) soil, the intensity of soil ammonification, nitrification, N fixation and cellulose decomposition decreased by 43.2%~71.1%, 70.1%~92.1%, 58.7%~87.8% and 55.3%~79.8% respectively. The decrease of soil microbial activity weakened the circulation rate and energy flow of C and N nutrients in the soil of the mining area.

Determination of trace potassium permanganate in tap water by solid phase extraction combined with spectrophotometry

A simple solid phase extraction (SPE) coupled with spectrophotometric method was developed for determination of trace permanganate (MnO₄ ^-) in water. Commercial reagent polyamined-6 powder was used as SPE stationary phase to retain MnO₄ ^- which is based on the fact that MnO₄ ^- can be adsorbed on polyamide 6 (PA-6) sorbent as water samples flow through the SPE cartridge. 3,3',5,5'-tetramethylbenzidine (TMB) were used both as eluent solution and chromogenic agent to convert the adsorbed MnO₄ ^- into Mn²⁺ and generate blue oxidized product with high molar absorptivity. Quantification of MnO₄ ^- could be obtained by spectrophotometric detection of the resulting solution flow out of the SPE cartridge. The extraction and detection variables was optimized to maximize the absorbance of the TMB oxidized product. Under optimized conditions, this method provided linear dynamic ranges of 0.01-1 μmol L^-1 for MnO₄ ^- with preconcentration of 100 mL water sample. The limits of detection (3S_b/m) of this method in deionized water were calculated to be 5.1 nM, and the relative standard deviations were determined to be 3.2% (C = 0.1 μmol L^-1, n = 5). This method has been applied to the determination of MnO₄ ^- in spiked tap waters and satisfactory recovery was obtained.

A fluorescent probe for sequential sensing of MnO4− and Cr2O72− ions in aqueous medium based on a UCNS/TMB nanosystem

Distinguishable and sequential detection of MnO₄⁻ and Cr₂O₇²⁻ was realized by the reactions above and IFE between UCNS and oxTMB.