Development of a chromatographic method for optimizing the thiol-maleimide coupling of polyoxometalate-polymer hybrids.

The covalent attachment of polyoxometalates (POMs) to polymers has been developed as a strategic approach for the advancement of POM-based hybrid materials with versatile applications. In this study, we utilized thiol-maleimide Michael addition to investigate the kinetics and efficacy of the "one-to-one" conjugation between Keggin type POM and polystyrene. We explored the effects of solvent polarity, catalyst, molecular weight of PS and synthetic strategies on the reaction kinetics and efficiency, by means of reverse-phase high-performance liquid chromatography (RP-HPLC). A series of comparative analysis affirmed the superior efficiency of the one-pot method, particularly when facilitated by the addition of a high-polarity solvent and an excess of maleimide. These findings offer valuable insights into the intricate interplay between reaction conditions, kinetics, and selectivity in thiol-maleimide reactions of POMs and polymers. They hold profound implications for advancing the study of POM-based multifunctional materials and the synthesis of complex hybrid molecules.

Corner-opening and corner-capping of mono-substituted T8 POSS: product distribution and isomerization.

We applied chromatographic and spectroscopic techniques to revisit the product distribution of the corner-opening and corner-capping reactions of monosubstituted T8 POSS. The monosubstituted Si is more likely to be removed than the remaining seven Si atoms during the corner-opening. After the corner-capping, the yield of monosubstituted T8 POSS is much higher than the yields of the ortho- and meta-isomers of disubstituted T8 POSS, and the para-isomer is negligible.

Process tracing of PCDD/Fs from economizer to APCDs during solid waste incineration: Re-formation and transformation mechanisms.

The emission of PCDD/Fs is a crucial factor for the aggravation of the Not-In-My-Back-Yard (NIMBY) syndrome, especially for the incineration plants that fail to meet the emission standard. It is well known that physicochemical processes in the boiler can notably affect the discharge of dioxins, especially under transient, non-steady conditions. However, few studies paid attention to the important operational parameters that influence PCDD/Fs formation and transformation in the boiler when an incinerator is in its daily steady operation. In this study, 36 samples were analyzed to achieve process tracing of PCDD/Fs. The concentration, congener profile and vapor/solid partitions of PCDD/Fs from the economizer to air pollution control devices (APCDs) under two typical steady conditions were investigated. Results indicated that increasing air supply aggravated the formation of PCDD/Fs, disturbed the vapor/solid partitions, and triggered a substandard emission. Quantitative structure-activity relationship (QSAR) modeling was firstly performed for the formation mechanism and orbital energy factors were identified as dominating factors. Besides, the removal rates of PCDD/Fs significantly correlated with the saturated vapor pressure and proportions of different isomers. This study is beneficial for operators to optimize relevant operational parameters of the incineration plants so as to get rid of substandard problems.

Seasonal occurrence, removal and risk assessment of 10 pharmaceuticals in 2 sewage treatment plants of Guangdong, China.

A long-term investigation, which covered 10 sampling campaigns over 3 years, was performed to evaluate the occurrence, removal and risk of 10 pharmaceuticals in 2 full-scale sewage treatment plants (STPs) in Guangdong, South China. Target pharmaceuticals except for clofibrate and ibuprofen were detected in every sample, with mean concentrations of 12.5-685.6 and 7.9-130.3 ng/L in the influent and effluent, respectively. Salicylic acid was the most abundant compound in both the influents and effluents in the two STPs. For most pharmaceuticals, the seasonal variation in the influent showed the highest concentrations in January and lowest concentrations in July due to their consumption and rainfall. Ibuprofen and fenoprofen presented high removal rates (>90%) and some of the targets such as gemfibrozil, mefenamic acid, tolfenamic acid and diclofenac were detectable with significantly higher mass loads in effluents than in influents. Studies of the five efficiently eliminated pharmaceuticals show that the primary treatment and secondary treatment contributed to most pharmaceutical removal, the anoxic tank made a negligible contribution to their elimination. According to the results produced from the calculation of the risk quotient, only diclofenac might pose a risk to the aquatic environment.

Emission characteristics of PCDD/Fs in stack gas from municipal solid waste incineration plants in Northern China.

Emission characteristics including congener's profile, gas emissions and toxic equivalent concentration (TEQ) indicators of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in 57 stack gas samples from 6 municipal solid waste incinerators (MSWIs) in Northern China were investigated by gas chromatography-high resolution mass spectrometry (HRGC-HRMS). Additionally, PCDD/Fs formation mechanisms from the MSWIs were briefly discussed. Results revealed that the concentrations and equivalent concentrations of PCDD/Fs emissions in stack gas from 6 MSWIs were in the range of 0.11-2.53 ng Nm-3 and 0.007-0.059 ng TEQ Nm-3, respectively. The emission factors of PCDD/Fs from 6 MSWIs varied from 0.027 to 0.225 µg I-TEQ tonne-1, with a mean value of 0.17 µg I-TEQ tonne-1 waste, which was estimated to an annual emission of 234.96 mg I-TEQ of PCDD/Fs from 6 MSWIs to the atmosphere. O8CDD, O8CDF and 1,2,3,4,6,7,8-H7CDD were the indicatory compounds of PCDD/Fs to apportion the sources of PCDD/Fs in environmental medium especially in ambient environment of MSWIs. 1,2,3,7,8,9-H6CDF and 1,2,3,4,7,8-H6CDF can be used as TEQ indicators for monitoring PCDD/Fs emission. Based on the positive matrix factorization (PMF) model, eight factors were extracted by the PMF analysis. Formation of low-chlorinated PCDDs (1,2,3,7,8-P5CDD, 1,2,3,4,7,8-H6CDD, 1,2,3,6,7,8-H6CDD and 1,2,3,7,8,9-H6CDD) possessed strong correlation, and the chlorophenols maybe the important precursors of low-chlorinated PCDDs, which were generated within the low chlorinated content. Penta- and hexa-PCDFs formation in stack gas from MSWI may block catalytic sites for PCDFs formation from carbon. Meanwhile, possible formation mechanisms of high-chlorinated PCDDs (hepta- and octa-PCDDs) and high-chlorinated PCDFs (hepta- and octa-PCDFs) were respectively dependent.

Removal of naproxen and bezafibrate by activated sludge under aerobic conditions: kinetics and effect of substrates.

Naproxen and bezafibrate fall into the category of pharmaceuticals that have been widely detected in the aquatic environment, and one of the major sources is the effluent discharge from wastewater treatment plants. This study investigated the sorption and degradation kinetics of naproxen and bezafibrate in the presence of activated sludge under aerobic conditions. Experimental results indicated that the adsorption of pharmaceuticals by activated sludge was rapid, and the relative adsorbabilities of the two-target compounds were based on their log Kow and pKa values. The adsorption data could be well interpreted by the pseudo-second-order kinetic model. The degradation process could be described by the pseudo-first-order kinetic model, whereas the pseudo-second-order kinetics were also well suited to describe the degradation process of the selected compounds at low concentrations. Bezafibrate was more easily degraded by activated sludge compared with naproxen. The spiked concentration of the two-target compounds was negatively correlated with k1 and k2s , indicating that the substrate inhibition effect occurred at the range of studied concentrations. Chemical oxygen demand (COD) did not associate with naproxen degradation; thus, COD is not an alternative method that could be applied to investigate natural organic matter's impact on degradation of pharmaceuticals by activated sludge.