Zhiwen Cheng

Synthesis of a stable magnesium-impregnated biochar and its reduction of phosphorus leaching from soil

Biochar improves soil fertility and promotes long-term terrestrial carbon sequestration. However, biochar seems not to be stable enough due to physical, chemical and biological reactions. In this study, a novel, stable, and magnesium (Mg)-impregnated biochar was prepared from cow dung and applied to decrease P leaching from soil. XPS, FTIR, XRD, SEM and EDS were used to evaluate the effect of modification and phosphorus(P) sorption on the oxidation resistance of biochar. The results showed that the oxidation resistance of the Mg-impregnated biochar was improved by the formation of MgO on its surface. The soil column experiment indicated that the Mg-impregnated -biochar decreased P loss from leaching by 89.25%. In addition, the available P content of the soil surface layer under Mg-impregnated biochar treatment increased by 3.5-fold relative to that under the control treatment. P sorption also enhanced the oxidation resistance of biochar. The relative contents of CO, CO, and COOH on the surface of P-laden biochar was 20.97% and was lower than those on the surface of biochar without P sorption (33.15%). Oxidation resistance was enhanced by the formation of new MgP crystals, which prevented the oxidation of CC, CC, and CH into CO, CO, and COOH, respectively, by acting as a physical barrier between the biochar surface and oxygen. The results of XRD, SEM and EDS provided evidence for the formation of MgP crystals. Overall, results indicated that the Mg-impregnated biochar can reduce P leaching loss from soil and has enhanced stability.

2D-QSAR and 3D-QSAR simulations for the reaction rate constants of organic compounds in ozone-hydrogen peroxide oxidation

Synergistic oxidation of ozone (O3) and hydrogen peroxide (H2O2) is an effective water treatment for the elimination of organic pollutants. In this study, 23 organic compounds were conducted to study the reaction rate constants during O3-H2O2 oxidation. Then, two- and three-dimensional quantitative structure-activity relationship (QSAR) models were established to investigate the factors influencing the reaction rate constants by using multiple linear regression method and comparative molecular similarity index analysis (CoMSIA) method, respectively. Both of the two models showed good performance on predicting the reaction rate constants, the associated statistical indices of 2D-QSAR and 3D-QSAR models were R2 = 0.898 and 0.952, q2 = 0.841 and 0.951, Qext2 = 0.968 and 0.970, respectively. But varied in the influence factors, as for the 2D-QSAR model, three quantum chemical parameters, included dipole moment, the largest change of charge in each atom during the nucleophilic attack, the maximum positive partial charge on a hydrogen atom linked with a carbon atom affected the reaction rate. While in the 3D-QSAR model, the electrostatic field played the most important role in evaluating the reaction rate with the contribution of 35.8%, followed by hydrogen bond acceptor and hydrophobic fields with the contribution of 24.9% and 23.2%, respectively. These two models provided predictive tools to study the influencing factors for the degradation of organics and might potentially be applied for estimating the removal properties of unknown organics in O3-H2O2 oxidation process.

Supercritical water oxidation of 2-, 3- and 4-nitroaniline: A study on nitrogen transformation mechanism

Supercritical water oxidation (SCWO) of 2-, 3- and 4-nitroaniline (NA) was investigated under residence time of 1-6 min, pressure of 18-26 MPa, temperature of 350-500 °C, with initial concentration of 1 mM and 300% excess oxygen. Among these operating conditions, temperature and residence time played a more significant role in decomposing TOC and TN than pressure. Moreover, the products of N-containing species were mainly N2, ammonia and nitrate. When temperature, pressure and retention time enhanced, the yields of NO3- and org-N were reduced, the amount of N2 was increasing, the proportion of NH4+, however, presented a general trend from rise to decline in general. The experiment of aniline/nitrobenzene indicated that TN removal behavior between amino and nitro groups would prefer to happen in the molecule rather than between the molecules, therefore, the smaller interval between the amino and nitro group was the more easily to interreact. This might explain the reason why TN removal efficiency was in an order that 2-NA > 3-NA > 4-NA. The NH4+/NO3- experiment result demonstrated that ammonia and nitrate did convert into N2 during SCWO, however, the formation of N2 was little without auxiliary fuel. Density functional theory (DFT) method was used to calculate the molecular structures of 2-, 3- and 4-NA to further explore reaction mechanism, which verified that amino group was more easily to be attacked than nitro group. Based on these results, the conceivable reaction pathways of 2-, 3- and 4-NA were proposed, which contained three parts, namely denitrification, ring-open and mineralization.