Wangjin Yang

Heterogeneous Photochemical Conversion of NO2 to HONO on the Humic Acid Surface under Simulated Sunlight

The poor understanding of HONO sources in the daytime highlights the importance of the heterogeneous photochemical reaction of NO2 with aerosol or soil surfaces. The conversion of NO2 to HONO on humic acid (HA) under simulated sunlight was investigated using a flow tube reactor at ambient pressure. The uptake coefficient (γ) of NO2 linearly increased with irradiation intensity and HA mass in the range of 0-2.0 μg/cm(2), while it decreased with the NO2 concentration. The HONO yield was found to be independent of irradiation intensity, HA mass, and NO2 concentration. The temperature (278-308 K) had little influence on both γ and HONO yield. Additionally, γ increased continuously with relative humidity (RH, 7-70%), and a maximum HONO yield was observed at 40% RH. The heterogeneous photochemical reaction of NO2 with HA was explained by the Langmuir-Hinshelwood mechanism.

Photocatalytic activity of CaTiO3 synthesized by solid state, sol–gel and hydrothermal methods

The structures and compositions of CaTiO3 samples synthesized by solid state, sol–gel, and hydrothermal methods were characterized by various means such as X-ray diffractometer, scanning electron microscope, Brunauer–Emmett–Teller, Fourier transform infrared spectrometer, Raman spectra, X-ray photoelectron spectroscopy, and UV–vis diffuse reflection spectra. Photocatalytic activity of CaTiO3 was investigated via measuring the photodegradation of methylene blue. As-prepared samples by three methods were orthorhombic CaTiO3, showing heterogeneous sizes and diverse morphologies. Functional groups including Ti–O, N–O, and OH were detected for three CaTiO3 samples. In particular, the XPS spectra suggested the presence of Ti–O–N or Ti–N–O structure in CaTiO3 lattice, indicating that N in air or Ca(NO3)2·4H2O (Ca source) may lead to forming N-doped CaTiO3 by solid state method or sol–gel and hydrothermal methods. Photocatalytic activity of CaTiO3 prepared by the hydrothermal method was the highest among three CaTiO3 samples, whereas it was lower than that of TiO2.Graphical Abstract

Evaluation of the role of inherent Ca2+ in phosphorus removal from wastewater system

The role of inherent Ca(2+) in phosphorus removal from wastewater was evaluated by batch tests. Precipitates were characterized by an X-ray diffractometer (XRD), Fourier transform infrared spectrophotometer (FT-IR) and scanning electron microscope with an energy dispersive spectrometer (EDS) system. Effects of inherent Ca(2+) on phosphorus removal through basic oxygen furnace slag (BOFS) were also analyzed. The results show that upon adjusting the pH to higher than 7.0, inherent Ca(2+) can remove phosphorus from wastewater and form Ca-P precipitates. Residual phosphorus exhibited a linear decreasing trend with increasing the pH from 7.0 to 10.0 and then remained unchanged at higher pH than 10.0. EDS determined that the precipitates contained the elements Ca, P and O. FT-IR spectra demonstrated that the functional groups of precipitates involved PO4(3-), OH(-) and CO3(2-). XRD indicated that the precipitates may consist of CaCO3 and some Ca-P phosphates such as CaHPO4, Ca4H(PO4)3, Ca3(PO4)2, and Ca5(PO4)3(OH). During the removal process of phosphorus by BOFS, due to the presence of inherent Ca(2+) in wastewater, the removal efficiency and rate of phosphorus increased by 15.5% and by a factor of about 3.0, respectively.

Investigation of the phosphorus removal capacities of basic oxygen furnace slag under variable conditions

ABSTRACT Effects of reaction time, initial phosphorus concentration, basic oxygen furnace slag (BOF-slag) dosage and size, and temperature on the phosphorus removal capacities (PRCs) of BOF-slag have been investigated in detail through batch tests. Weakly bound phosphorus, Fe- and Al-associated phosphorus, and Ca-associated phosphorus from fresh and reacted BOF-slag were analysed using sequential chemical extraction processes. It was determined that the PRCs of BOF-slag increased with the increase of initial phosphorus concentration and temperature while it decreased with the increase of BOF-slag dosage and size. The phosphorus removed by BOF-slag was primarily assigned to weakly bound phosphorus and Ca-associated phosphorus. Weakly bound phosphorus showed a significant decrease with the increase in all experimental parameter values. However, Ca-associated phosphorus exhibited a prominent increase with increasing reaction time, initial phosphorus concentration, and temperature. These demonstrate that experimental parameters can simultaneously affect the PRCs of BOF-slag and the ways of phosphorus removal by BOF-slag.

Enhanced photochemical conversion of NO2 to HONO on humic acids in the presence of benzophenone

The photochemical conversion of NO2 to HONO on humic acids (HA) in the presence of benzophenone (BP) was investigated using a flow tube reactor coupled to a NOx analyzer at ambient pressure. BP significantly enhanced the reduction of NO2 to HONO on HA under simulated sunlight, as shown by the increase of NO2 uptake coefficient (γ) and HONO yield with the mass ratio of BP to HA. The γ and HONO yield on the mixtures of HA and BP obviously depended on the environmental conditions. Both γ and HONO yield increased with the increase of irradiation intensity and temperature, whereas they decreased with pH. The γ exhibited a negative dependence on the NO2 concentration, which had slight influences on the HONO yield. There were maximum values for the γ and HONO yield at relative humidity (RH) of 22%. Finally, atmospheric implications about the photochemical reaction of NO2 and HA in the presence of photosensitive species were discussed.

Significant HONO formation by the photolysis of nitrates in the presence of humic acids

The generation of HONO and NO2 by the photolysis of nitrates in the presence of humic acids (HA) was measured under various conditions. The photolysis experiments of HA, KNO3 and KNO3/HA under simulated sunlight was carried out by a flow tube reactor at ambient temperature and pressure. HONO and NO2 were major products by the photolysis of KNO3. By contrast, the photolysis of HA and KNO3/HA mainly generated HONO. HA significantly enhanced the formation of HONO during the photolysis process of KNO3. With increasing the KNO3 mass, the HONO formation rate (RHONO) on KNO3/HA increased while the photolysis rate normalized by the KNO3 mass exhibited an opposite trend. RHONO on KNO3/HA linearly increased with irradiation intensity (88-262 W/m2) and relative humidity (7-70%), whereas it linearly decreased with the pH (pH = 2-12). In addition, the reaction paths of the HONO formation by the photolysis of nitrates in the presence of HA were proposed according to experimental results. Finally, atmospheric implications of the enhanced HONO formation by the photolysis of nitrates in the presence of HA were discussed.