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Heterojunction formation and morphology control have always been regarded as effective ways to improve the performance of visible-light-driven photocatalysts. In this study, a new facile strategy was applied to synthesize the Z-scheme GO/AgI/Bi2O3 heterojunction, where polyvinyl pyrrolidone (PVP) and γ-methacryloxypropyl trimethoxy silane (KH-570) were used to modulate the morphologies. Methyl orange and tetracycline hydrochloride were chosen as target contaminants to evaluate the photocatalytic properties of samples and the results revealed that 2% GO/AgI/Bi2O3 exhibited the best photocatalytic performance under visible-light irradiation. The enhanced photocatalytic activity can mainly attribute to Z-scheme heterojunction formed by the deposing of AgI and GO as well as the sufficient heterogeneous interfaces resulted from the improved morphology, which have effectively promoted the separation and transfer of electron-hole pairs. To deeply realize the enhanced performance of GO/AgI/Bi2O3 photocatalysts, the reaction kinetics, trapping experiments and photocatalytic mechanism were deduced.

Process-based samples of VOCs were collected in three prebaked anode manufacturers to analyze the emission characteristics of calcining and baking process. Besides, the ratios of diagnostic VOCs were investigated, and the OH loss rate (LOH), ozone potential formations (OFP) and secondary organic aerosol formations potential (SOAFP) of VOCs were calculated to estimate environmental impact. Results shows that the VOCs concentrations emitted from calcining and baking were in the range of 213.5–1081.8 μg/m3, and 2530.1–26774.8 μg/m3, respectively. Aromatics accounted 51.8% and 68.7% and naphthalene accounted 22.6% and 30.7% for total VOCs in calcining or baking, respectively. VOCs emission factors of prebaked anode manufacturing industry were averaged 0.198 ± 0.153 kg/t, and at least 3.2 ± 2.5 kt and 5.6 ± 4.4 kt VOCs were released in China and global, respectively, in 2017. The measured diagnostic ratios of VOCs such as benzene, toluene, xylene, ethylbenzene, naphthalene, styrene, and CS2 were expected to be useful for source identification. VOCs emitted from baking had more adverse impact on environment than calcining, and whether in calcining or baking, aromatics were the largest contributor to LOH, OFP and SOAFP, means that should be controlled primarily.

The series Ag-AgI/BiOI-Bi2O3 visible-light-driven photocataslyts were successfully synthesized by solvothermal method. The as-synthesized samples were systematically characterized by XRD, SEM, TEM, EDS, BET, XPS, FR-IR, UV–vis DRS, photoelectrochemical measurements and EPR. The formation mechanism of the new composite photocataslyts was investigated and the simulate formation process had been illustrated. The photocatalytic properties of the samples were evaluated by degradation of methyl orange under visible-light irradiation. The results shown that the 30% Ag-AgI/BiOI-Bi2O3 photocataslyts possessed the best photocatalytic activity and the kinetics reaction models were followed pseudo-first-order kinetics. The enhanced photocatalytic performance could be attributed to the effective separation and transfer of electron–hole pairs resulting by the deposing of Ag-AgI nanoparticles and Bi2O3. The photocatalytic mechanism was deduced by trapping experiments and EPR, and the results demonstrated that h+, OH, O2− radicals played different roles in the degradation. Furthermore, a new Z-scheme multi-heterojunction mechanism was proposed basing on the results of trapping experiments and EPR.

To investigate the formation of haze during the cold season, continuous ambient air measurements were taken at an urban site in Zhengzhou from October 10, 2016 through December 31, 2016 using a single particle aerosol mass spectrometer. In total, 4,099,800 particles were analyzed and classified into eight major particle types: elemental carbon (EC, 36.7%), organic carbon (OC, 30.0%), ECOC (8.6%), K-rich (13.0%), levoglucosan (1.2%), metal (2.2%), NH4-K (2.1%), and dust (6.2%). By combining these measurements with correlation analysis and wind data, particle sources were determined to be vehicles, industrial emissions, coal combustion, biomass burning, secondary aerosols, agriculture, and dust. Additionally, analysis of mixing states indicated that particles underwent substantial aging and secondary OC particles were dominant OC species. Temporal profiles of meteorological parameters, mixing states, and particle types during a typical haze episode revealed that EC and OC particles were dominant components during haze formation, and a northeastern transport route (Anyang-Zhengzhou and Puyang-Xuchang) for OC particles was identified by potential source contribution function and concentration weighted trajectory analysis. Relatively higher humidity and lower temperature favored the formation of secondary inorganic aerosol. Wind direction and speed determined the transport, formation, and elimination of stagnant weather conditions. In sum, heavy haze during the cold season in Zhengzhou was observed due to extensive aerosol aging under adverse weather conditions (i.e., northeastern wind direction, wind speed 60%, temperature inversion, and uniform pressure field).

Size-resolved samples were collected using a 14-stage impactor during four seasons in Zhengzhou and analyzed for 26 elements to calculate the health risks from atmospheric particle-bound metals. High concentrations of heavy metals were observed in ultrafine (10.2 (Ni)–66.9 (Cd) ng m−3) or submicrometer (11.4 (Ni)–134 (Pb) ng m−3) mode in winter. Two size-dependent models were used to estimate the deposition of inhaled toxic metals in various regions of the human respiratory system. Results show that heavy metals deposited in the alveolar region ranged from 7.6 (As)–375 (Al) ng m−3 and were almost concentrated in ultrafine and fine modes. Cd (2.2–8.6) may cause accumulative non-carcinogenic health effects on children, and Cr (1.0 × 10−4–2.2 × 10−4) may lead to carcinogenic health risks for nearby residents around the sampling site. The major sources by principal component analysis that contributed to Cr and Cd in ultrafine and fine particles were coal combustion, vehicular and industrial emissions. The atmospheric dry deposition fluxes of Cr and Cd were between 0.7 and 1.9 μg m−2 day−1 calculated by a multi-step method. From the environmental and public health perspective, environmental agencies must control the emission of heavy metals in the atmosphere.

The visible-light-driven Fe3O4/BiOI n-p heterojunction photocatalysts were successfully synthesized by a facile and economical solve-thermal method. The as-prepared samples were systematically characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectra, and vibrating sample magnetometer. The methyl orange and sulfadiazine sodium salt were taken as the model pollutants to estimate the photocatalytic activities of the Fe3O4/BiOI composites with different Fe3O4 contents. The results revealed that the photocatalytic properties of photocatalysts within the appropriate loading range were superior to pure BiOI. Among them 7 wt% Fe3O4/BiOI composite exhibited the highest photocatalytic activity both on degradation of MO and SD-Na. The increase in photodegradation activity may be attributed to the moderate loading of Fe3O4, which could promote the separation of electron–hole pairs effectively. Furthermore, the introducing of Fe3O4 provides the composite a good magnetic property, which greatly promotes the practical application of Fe3O4/BiOI composite photocatalysts in water purification.

The magnetic Co0.5Zn0.5Fe2O4 incorporated Ag3PO4 photocatalysts were fabricated by facile sol-gel and hydrothermal route. The resulting Co0.5Zn0.5Fe2O4/Ag3PO4 composites were characterized by XRD, 1 SEM, 2 UV–vis DRS, 3 FT-IR 4 and VSM. 5 The results indicated that the magnetically separable composites with good dispersity showed a strong absorption in the uv–vis region and the saturation magnetization was 85.25 emu g−1. Anionic dye methyl orange (MO) and tetracycline hydrochloride (TCH) were used to evaluate the activity of the photocatalysts. The result revealed that the magnetic composites exhibited enhanced photocatalytic activity and stability under the visible light irradiation. The ·OH and ·O2- radicals were found to be the major active species during the photodegradation of TCH, while·O2- played the important role in photodegrading MO. And a Z-scheme mechanism for the enhanced photocatalytic process was proposed.

Co0.5Zn0.5Fe2O4/AgBr hybrids with p-n heterojunction were prepared by a facile sol-gel and hydrothermal method. And the samples with different AgBr contents were characterized by XRD, 1 SEM, 2 UV–vis DRS 3 and FT-IR. 4 The degradation capability of the photocatalysts were evaluated under visible light and used methyl orange (MO) as a target contaminant. All the composites possessed the magnetic properties of Co0.5Zn0.5Fe2O4 and also exhibited high photocatalytic activity of AgBr. Among the prepared photocatalysts, the hybrids prepared with 0.5 g AgNO3 exhibited the highest photocatalytic efficiency. The increase photocatalytic activity of Co0.5Zn0.5Fe2O4/AgBr hybrids might be associated with the formation of suitable internal structures between Co0.5Zn0.5Fe2O4 and AgBr. And a possible photocatalytic mechanism of the Co0.5Zn0.5Fe2O4/AgBr hybrids was proposed.

A dual Z-scheme carbon-bridged g-C3N4/BiOI-Bi2O3 photocatalyst were synthesized by simple solvothermal and calcination methods. The physical and chemical properties of prepared samples were explored via a series of characterization and Density Functional Theory (DFT) calculations. The formation mechanism of the composite photocatalyst was systematically studied and the formation process was simulated. Under the irradiation of visible light, 10% carbon-bridged g-C3N4/BiOI-Bi2O3 exhibited the best photocatalytic performance. And the kinetics reaction model was followed pseudo-first-order kinetics. Moreover, the possible TC degradation pathways were established based on LC-MS. The enhanced photocatalytic activity was mainly attributed to the dual Z-scheme heterojunction formed by carbon-bridged g-C3N4 deposition on the surface of Bi2O3 and BiOI and a higher charge transfer rate of carbon-bridged g-C3N4, which effectively promoted the separation and transfer of electron-hole pairs. The trapping experiments were carried out to further explore its photocatalytic mechanism. This work provided an in-depth understanding of g-C3N4 and bismuth-based catalysts.

The metal defect engineering is the crux to accomplish the goal of local electronic regulation, which is an important factor for visible light to drive photocatalyst performance. In this paper, the solvothermal-precipitation method was used to reduce Bi in situ via the reducer glucose to construct Ag-AgI/Bi-Bi2O2CO3-OVs heterojunction. The Ag-AgI/Bi-Bi2O2CO3-OVs composite photocatalyst has excellent photoresponse ability and fast charge carrier separation. In addition, the powerful S-scheme heterojunction retains the original redox capability of the components. The unique lawn-like structure exhibits favorable surface scattering and reflection, which promotes efficient separation of photoinduced charge carriers. Especially, 30% Ag-AgI/Bi-Bi2O2CO3-OVs exhibits brilliant photocatalytic performance for the degradation of tetracycline, which is 4.85 times and 1.15 times higher than the original Bi2O2CO3 and AgI, respectively. The enhanced photocatalytic activity mainly attributes to the presence of oxygen vacancies, the sensitization of Ag-AgI, the double surface plasmon resonance (SPR) effect, and the heterogeneous interface due to the improved morphology, which effectively inhibits the recombination of electron-hole pairs. This work provides a new perspective for the reasonable construction and simple synthesis of high-performance Bi-based semiconductor photocatalysts.

The CuFe2O4 and CuFe2O4/AgBr composites with different CuFe2O4 contents were prepared by a facile sol-gel and hydrothermal method, respectively. The as-synthesized photocatalysts were characterized by means of powder X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectrum (UV–vis DRS). Their magnetic properties, photocatalytic degradation activities on methyl orange (MO) and tetracycline hydrochloride (TC) solution and photocatalytic mechanism were investigated in detail. The results revealed that the CuFe2O4/AgBr composites exhibited significantly higher photocatalytic activities than the pure CuFe2O4. The enhanced photocatalytic activity could be attributed to the matched band structure of two components and more effective charge transportation and separations. In addition, the quenching investigation of different scavengers demonstrated that h+, OH, O2− reactive species played different roles in the decolorization of MO and degradation of TC.

Interfacial charge transfer acts as a linchpin role in the research of photogenerated carrier recombination and photocatalysis. In this work, AgBr/Bi2O2CO3 was constructed to explore the structure-activity relationship between heterostructure and catalytic mechanism. The excellent photosensitizer silver bromide nanoparticles were immobilized on the surface of the Bi2O2CO3 hollow pineal-like via a simple hydrothermal method and deliberated the formation mechanism of the heterostructure. The heterostructures were characterized through XRD, BET, XPS, SEM, TEM, EDX, UV–Vis DRS, EIS, PT and TOC. Research demonstrates that owing to the distinct layered structure exhibits fine surface scattering and reflection. It has excellent degradation performance for dyes and PPCPs wastewater and can be completely degraded in a short time. Simultaneously, the introduction of the Z-type mechanism into the p-n type heterojunction photocatalyst, together with the joint contribution of the Schottky barrier, extremely facilitates the charge separation, illustrating brilliant photocatalysis active. Furthermore, Free radical capture experiments certificate that •O2− and h+ are the chief active species in the decomposition of organic pollutants, and the potential photocatalytic mechanism is considered. The consequences of this work will furnish a fresh perspective for the configuration of high-performance visible light-responsive photocatalysts.

The three-dimensional (3D) flower-shaped layered Bi5O7I nanosheets exhibited tremendous potential in wiping out hazardous organics of sewage due to appropriate band structure and rich surface for attachment of reactants, modified with CuBi2O4 (CBO) and reduced graphene oxide (rGO) further enhancing its photocatalytic effects. Herein, a novel, stabilized and efficient CBO/Bi5O7I@rGO photocatalyst was constructed via sequential hydrothermal process, and the microstructures, physicochemical and optical properties were further researched by serial means such as XRD, XPS, FESEM-EDS, TEM, UV–vis DRS, PT, EIS and physical absorption. SEM and TEM manifested that the composite was successfully prepared and gossamer rGO as a co-catalyst, which is not only conducive to the separation of photo-generated carrier but also facilitates photocatalytic removal pollutants. Furthermore, the photodegradation tests indicated that CBO/Bi5O7I@1.5% rGO sample displayed the highest removal rates towards contaminations such as tetracycline hydrochloride (91%), Rhodamine B (77%) and ciprofloxacin (92%) under visible-light, respectively. Besides, the addition of higher initial concentrations and certain anions inhibited photocatalytic efficiency, which perhaps was due to greater competition with contaminations towards active radicals. Finally, the capture experiment and electron spin resonance (ESR) test certified that superoxide radicals ( · O 2 - ) are the direct active group, whereas the holes (h+) and hydroxyl radicals ( · OH) exert a supporting role. This work could offer an actual and doable design for constructing of efficient Z-scheme system using rGO as an auxiliary catalyst to sewage remediation.

Ion-doped semiconductor photocatalysts were considered to be an important strategy to improve photocatalytic performance. A simple one-step solvothermal method was used to prepare flower ball-shaped Bi4O5I2 nanomaterials modified by Nickel. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra, photocurrent response and EIS Nyquist plots were used to explore its structural composition and photoelectrochemical properties. The photocatalytic activity was studied by simulating the degradation of tetracycline under visible light. The degradation results showed that photocatalytic effect of 5 wt% Ni-doped Bi4O5I2 was the best among the samples, and the degradation rate was 91%. The capture experiment shown that the vital active radical is O2–. The final results shown that Ni-doping improved the charge separation efficiency and the specific surface area of the material, and it is proved by Raman that Ni-doping formed shallow traps on the surface of Bi4O5I2, which promoted the separation and transfer of carriers and improved the photocatalytic activity. This work can provide a reference for the subsequent development of bismuth-based photocatalysts.

In this work, a series of 3D hierarchical γ-AgI/Bi2WO6 (AB) Z-scheme heterojunctions with intimate interface contact was synthesized by facile hydrothermal and precipitation method. The optimal proportion of γ-AgI/Bi2WO6 exhibited superior photocatalytic property during the removal of Rhodamine B (RhB), tetracycline (TC) and ciprofloxacin (CIP). The outstanding photocatalytic capability was probably responsible for the intimate contact among Bi2WO6 flake ball-shaped and γ-AgI nanoparticle, which could heighten the responsive range of visible-light, promote the separation of photo-generated carriers and fully utilize the strong redox ability of composites. Additionally, the function of active species in the photodegradation was also researched through exploiting trapping tests and electron spin resonance experiments to reveal the vital effect of holes (h+) and superoxide anion radicals ( O2−). Moreover, the possible Z-scheme photocatalytic mechanism with an internal electric field was also proposed. This study spreads an effective strategy for reasonably devising the Bi2WO6-based photocatalytic system to decontaminate multiple pollutants.

A series of hierarchical AgIO3/BiVO4-GO photocatalysts was synthesized using a solvothermal-precipitation method. The composition, structure, morphology, optical and photoelectrochemical performance of as-obtained photocatalysts were systematically characterized by XPS, XRD, TEM, SEM, EDS, PL, UV–Vis DRS, PT, and EIS, respectively. The photocatalytic activity was evaluated by the degradation of tetracycline hydrochloride (TC) and Rhodamine B (RhB) under visible light irradiation. Experimental results exhibited the photocatalytic degradation activity of AgIO3/BiVO4 was significantly improved compared with pure AgIO3 and BiVO4. This may be due to the heterojunction formation of AgIO3 and BiVO4 and the introduction of GO, which accelerates the separation and migration of electron-hole pairs and reduce recombination. The h+ and •O2− was the key active species in the photocatalytic degradation process according to the trapping experiment. Furthermore, a potential photocatalytic mechanism was predicted based on experimental results.

The emission factors (EFs) and source profiles of polycyclic aromatic hydrocarbons (PAHs) in particulate matter (PM10 and PM2.5) from the prebaked anode industry were studied to fill the knowledge gap and provide data for emission inventory and source resolution. In 2018, three prebaked anode plants were selected in Central China, each having one calcining chimney as well as one baking chimney, and then 92 samples were collected from the stack gas of the six chimneys. The results of the study are as follows. (1) PM10 and PM2.5 from the prebaked anode industry contained 37–42% water-soluble ions, 16–20% elements, 11–17% organic carbon, and 9.2–14% elemental carbon. (2) The EFs for PAHs of PM10 and PM2.5 were 1146.1 ± 899.7 and 866.2 ± 1179.8 mg/(t aluminum produced), respectively. The EF for BaP was seven times lower than that given by the European Environment Agency (EEA), whereas those of BbF, BkF, and IcdP were 2–13 times higher than those given by the EEA. (3) Seven diagnostic ratios for PAHs, including Ant/(Ant+Phe), Flua/(Flua+Pyr), BaA/(BaA + Chr), IcdP/(IcdP+BghiP), Flu/(Flu+Pyr), Phe/Ant and BaA/Chr were discussed. Just by diagnostic ratio, it is hard to precisely distinguish between calcining and baking in prebaked industry. (4) The toxic equivalence of PMs in the baking stack gas in the prebaked anode industry was five times higher than that in the calcining stack gas, and PM2.5 showed higher potential toxicity risk than PM10.

This study aimed to investigate the characteristics of the water-soluble ions concentrations in atmospheric particulates. Highly time-resolved measurements of inorganic ions associated with PM2.5 were conducted from December 1, 2017 to February 28, 2018 in Zhengzhou. The hourly mean and standard deviation of PM2.5 concentration during the observation episodes were 108.2 ± 80.7 μg/m3. The hourly mass concentration of PM2.5 increased from 8 μg/m3 to 438 μg/m3 throughout the entire observation. The proportion of water-soluble inorganic ions in PM2.5 was 52.5% throughout the entire observation period. The ions existed mainly in the form of (NH4)2SO4 and NH4NO3. The average mass concentration ratio of NO3− to SO42− was 1.9 ± 0.8 throughout the entire observation period, which initially increased and then decreased with the increased pollution level. The average ratio of the molar equivalent concentration of [NH4+] to that of [NO3− + SO42−] was 1.14 ± 0.27, which decreased with the increased pollution level. Homogeneous reactions played an important role in the formation of nitrate, while, the heterogeneous reactions were important in the formation of sulfate. Both of the values of sulfur oxidation ratios (SOR) and nitrogen oxidation ratios increased with relative high humidity (RH) condition; especially, the SOR values sharply increased when the RH was above 50%. The results of potential source contribution function model demonstrated that the western and northeastern regions of Zhengzhou had a greater influence on PM2.5 pollution in Zhengzhou. All these results suggested that reducing the emission of precursors of secondary inorganic ions was highly important in controlling PM2.5 pollution in Zhengzhou.

A novel β-Ag2MoO4/BiVO4 heterojunction photocatalyst was synthesized via a simple precipitation method. The photocatalytic activity of photocatalysts was assessed by RhB (Rhodamine B) and TC (tetracycline hydrochloride) degradation. Furthermore, the Ag nanoparticles were produced during the photocatalytic degradation process facilitates the construction of Z-scheme system. The XRD, XPS, SEM, EDX, TEM, HR-TEM and BET measurements revealed the structure and morphology properties and the UV–Vis DRS, PL, PT and EIS were used to investigate the optical properties. The results exhibited that the β-Ag2MoO4/BiVO4 heterojunction photocatalyst possess higher photocatalytic activity than individual BiVO4 and β-Ag2MoO4. Furthermore, h+ was the most crucial active species in the β-Ag2MoO4/Ag/BiVO4 Z-scheme system according to the reactive species trapping experiments. The potential Z-scheme photocatalytic mechanism also was discussed based on experimental and characterization results. This work shows a simple method to construct Z-scheme heterojunction photocatalyst by self-assembly and demonstrates that photocatalytic technology has great application prospects for water purification.

a b s t r a c t To achieve high-performance, hierarchical plasmonic Ag/AgCl photocatalysts, a freeze-drying route was developed to form porous PVP-Ag + hybrid compounds, which were then transformed to hierarchical Ag/AgCl nanocrystals through a liquid-solid precipitation reaction followed by a partially photoreduction under ambient conditions. The PVP-Ag+ hybrid precursors and their final Ag/AgCl nanocrystals obtained were characterized by various techniques. The hierarchical Ag/AgCl nanocrystals obtained had an appar- ent size range of 156 ± 50 nm, and the surfaces of the large particles were covered with small nanocrystals with sizes of 33 ± 12 nm. The photocatalytic performance of the hierarchical Ag/AgCl nanocrystals was estimated by degradating organic dyes (i.e., RhB, MO, and MB) and alcohols (i.e., methanol and iso- propanol) under visible light (� ≥ 420 nm) and sunlight. The results indicated that the hierarchical Ag/AgCl nanocrystals obtained were efficient visible-light-driven photocatalysts in decomposing organic dyes, and their RhB photodegradation rates (∼0.97 min −1 ) was ∼54 times higher than that (∼0.018 min −1