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Persulfate (PS) activated by Fe(ii) has been widely investigated for degradation of contaminants. However, the Fe(ii)/PS systems used for actual contaminated groundwater remediation have been restricted by circulation of Fe(iii)/Fe(ii). Herein, an ascorbic acid (AA) enhanced Fe(ii)/PS system was developed for degradation of tetracycline (TC) contaminated groundwater. The influence of Fe(ii), AA, PS dosage and pH on degradation of TC was investigated, the free radicals produced in the reaction were identified and the reusability of Fe(ii) in the Fe(ii)/PS/AA system for degradation of TC was also evaluated. The results showed that AA significantly promoted the degradation of TC in the Fe(ii)/PS system, and a degradation rate of 86% for TC was achieved at 60 min. The dominant oxidant species for contaminant degradation in the Fe(ii)/PS/AA system is ˙OH. Appropriate Fe(ii), AA and PS dosage can improve the degradation rate of TC. Moreover, the degradation rate of TC in the Fe(ii)/PS/AA system under acidic conditions is higher than that under alkaline conditions. With the increase of reaction time, TC can also be completely degraded even with a little Fe(ii) or under alkaline conditions in the Fe(ii)/PS/AA system, and Fe(ii) showed a good reusability for the degradation of TC. Thus, the AA-enhanced Fe(ii)/PS system for the degradation of contaminants displays the advantages of less Fe(ii) consumption and a wide range of pH. This method provides a new strategy for in situ remediation of contaminated groundwater., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

This study aimed to achieve the controlled-release of bioactive ingredients in microcapsule pesticide delivery systems. A photothermal controlled-release microcapsule pesticide delivery system was constructed using chitosan and polydopamine (PDA) as the wall materials to encapsulate avermectin. All the prepared microcapsules were characterized by the methods of optical microscopy, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The slow-release, UV-shielding, photothermal performance, and the nematicidal activity of the prepared microcapsules were also systematically investigated. The results indicated that the prepared microcapsules had excellent slow-release and UV-shielding performance when further encapsulated with the PDA layer relative to those of the non-PDA-encapsulated products. The photothermal sensitivity of the AVM@CS/CMA/PDA composite microcapsule under the irradiation of near-infrared light (NIR) was dramatically enhanced with the photothermal conversion efficiency ( η ) of 14.93%. Furthermore, the nematicidal activity of the AVM@CS/CMA/PDA composite microcapsule system was effectively improved on exposure to the irradiation of a light-emitting diode (LED) full-spectrum light. The strategies used in this study for developing the photothermal controlled-release pesticide delivery system might play an important role on improving utilization of pesticides., Competing Interests: The authors report there are no competing interests to declare., (This journal is © The Royal Society of Chemistry.)

To improve the utilization rate of chlorfenapyr and make the wall material of chlorfenapyr microcapsules easily degradable, polylactide diol, toluene diisocyanate and 1,4-butanediol were used to prepare a chlorfenapyr microcapsule suspension by interfacial polymerization. The product was characterized by the methods of optical microscopy, scanning electron microscopy and Fourier-transform infrared spectroscopy. The results indicated that the microcapsule particles were spherical, with an encapsulation efficiency of 84.20%. The diluted product had good wetting and spreading abilities on cabbage leaves. Compared with other commercial formulations, the slow-release effect of the microcapsule suspension was more obvious and the release mechanisms conform to Fickian diffusion, with the release rate controllable by adjusting the external pH conditions. Furthermore, the wall material of the microcapsules showed good degradation performance in a phosphate-buffered solution. Microencapsulation by this method significantly increased the validity period of chlorfenapyr and the wall material was also degraded easily., Competing Interests: The authors report there are no competing interests to declare., (This journal is © The Royal Society of Chemistry.)

The chemical percolation devolatilization (CPD) model can simulate the formation of various products during the coal pyrolysis process and predict the products composition relatively accurately. In this study, the pyrolysis products of a typical low-rank coal were calculated using the CPD model, and several model improvements were proposed by combining the experimental results in a lab-scale pyrolysis system. The chemical structural parameters calculated from the Genetti correlations were verified by adjusting the initial fraction of char bridges ( c 0 ) from 0.098 to 0.25. A yield difference (Δ f tar ) was defined in this paper to analyze the consumption of tar fragments in the model, and it was found that the deviations between experiments and calculations resulted from the weak influence of crosslinking. A modification expression was adopted to amplify the tar consumption: , which improved the accuracy of the model on the tar yield with errors of less than ±0.5 wt%. Furthermore, this paper also developed a correlation in an exponential form about gas composition, which attempted to extend the application of the CPD coalification reference mesh for the coal away from interpolation triangles. The improved model by the correlation predicted CH 4 , CO, and CO 2 yields for this typical low-rank coal accurately in most cases. Compared with the original CPD model, the modified model showed better agreement with the experimental results and predicted 71.4% and 88.6% of the data points in this work within ±10% and ±20% errors, respectively., Competing Interests: The authors declare that there are no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Monoclinic BiVO 4 has been regarded as a promising photocatalyst for water splitting in recent years. In this research, the effects of Mo/W dopants near the surfaces of BiVO 4 on electron transport are investigated using first-principles calculations. We demonstrate that the additional electron introduced by Mo/W either in the bulk or near the surfaces forms a self-trapped small polaron. The polaron prefers to be localized on the transition metal ions in the subsurface layer when Mo/W is doped in the vicinity of the surfaces. The localized positions of polarons can be rationalized by the d-orbital energy levels of the transition metals and the variation of electrostatic potential. The concentrated electron polarons in the subsurface layer of BiVO 4 surfaces can build fast lanes for electron migration and mitigate the electron-hole recombination process, which underlines the importance of dopants near the surfaces as compared with those in the bulk., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this work, we explored a facile, scalable and effective method for substantially enhancing photocurrent and incident-photon-to-current efficiency of WO 3 thin-film photoanodes by a mild reduction treatment under low oxygen pressure. Experimental data from photoelectrochemical and electrochemical impedance spectroscopies have shown that such treatment can increase the charge carrier density on WO 3 photoanode surfaces resulting in improvements in hole collection efficiency and reduction in charge recombination. Despite a much thinner layer of WO 3 (about 500 nm) compared to those in other published studies, the electrodes exhibited an ultra-high photocurrent density of 1.81 mA cm -2 at 1.23 V vs. RHE. This current density is one of the highest ones among WO 3 -based photoanodes described in literature. The proposed surface modulation approach offers an effective and scalable method to prepare high-performance thin film photoanodes for photoelectrochemical water splitting., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Chemical kinetic modeling was applied to simulate N transformation in the pressurized oxy-fuel combustion process of pulverized coal. Modeling accuracy was validated by experimental data at different operation pressures. The key reaction paths from fuel-N to different N products were revealed by analyzing the rate of production. NO formation was synergistically affected by six elementary reactions, in which NCO and other intermediate species were involved. The reactions among N, NH, NH 2 , and NO were the key paths of N 2 formation. After pressurizing the combustion system, NO and N 2 contents decreased and increased, respectively. High operation pressure inhibited the diffusion of NO from the internal to the external part of char. This condition prolonged the residence time of NO inside the char, triggered a typical heterogeneous reaction between gaseous NO and unburned char, and reduced the conversion from fuel-N to NO. Moreover, modeling was performed to predict NO x emission in pressurized oxy-fuel combustion as a function of various operating parameters, including temperature and excess air and recycling ratios. This study may provide guidance for reducing NO x emissions and improving combustion efficiency in oxy-fuel combustion, and it can serve as a reference for industrial applications that involve pulverized coal combustion., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

This work aims to provide a comprehensive understanding of negative DC discharge under coal pyrolysis gas components (CO 2 , H 2 , N 2 , CH 4 , CO) and air. The characteristics of negative DC discharge were studied in a wire-cylinder configuration at an ambient temperature range of 20-600 °C by analyzing V - I characteristics, discharge photographs, and gas composition. With increasing temperature, corona onset voltage, spark breakdown voltage and operational voltage range for corona discharge decrease, but discharge current and electron current ratio increase. Discharge current of CO 2 is higher than that of air due to the difference of electronegativity. During CO 2 discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. However, during H 2 discharge, only glow discharge is observed. Temperatures significantly affect the capability of CO to attach electrons. The discharge characteristic of CO is similar to the electronegative gas media at 20 °C and the non-electronegative gas media when the temperature exceeds 350 °C. Chemical reactions and carbon generation are observed during the CH 4 and CO discharge process. The product of carbon filaments under the CH 4 gas medium leads to discharge current volatility and short circuit. These results assist in understanding the property of ESP at high temperatures., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Coal tar pitch was ground into powder and hydroformed with high pressure. After pre-oxidation, the pitch was activated by CO 2 at high temperature. The effects of different preparation conditions on the yield, pore structure and phenol adsorption capacity of activated carbon were investigated, and activated carbon prepared under suitable conditions had good adsorption performance. A pore volume of 1-10 nm is the main absorption structure according to the analysis of pore size distribution and phenol adsorption capacity. The activated carbon showed high mechanical strength through compressive strength tests. Graphite nanocrystals around 5 nm were observed in the TEM images, and it illustrates that grain refinement results in the high strength. These nanocrystal stacked structures are easier to make and enlarge pores by activation than graphite layer stacked structures. Surface functional groups are considered not to be the active sites of phenol adsorption as suggested by the results of FTIR and Boehm's titration, and acidic oxygen-containing functional groups are harmful to phenol adsorption, which happen to be removed in the reductive preparation atmosphere. The donor-acceptor complex mechanism can be ruled out, and the π-π interactions are considered the most likely mechanism. The Langmuir and Redlich-Peterson models are better fitted to the adsorption isotherms. Adsorption kinetics fit the intraparticle diffusion model best. Comparison of different activated carbons shows that suitable pore size is important for phenol adsorption. Thermodynamic parameters demonstrate that the adsorption process is spontaneous and exothermic, and the entropy increases. Pitch-based high-strength columnar activated carbon is an effective and low cost adsorbent for phenol wastewater treatment. This carbon nanocrystal material also provides a new direction for catalyst carriers., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)