Yaoyu Zhou

Modification of biochar derived from sawdust and its application in removal of tetracycline and copper from aqueous solution: Adsorption mechanism and modelling

Highly efficient simultaneous removal of Cu(II) and tetracycline (TET) from aqueous solution was accomplished by iron and zinc doped sawdust biochar (Fe/Zn-biochar). The mutual effects and inner mechanisms of their adsorption onto Fe/Zn-biochar were systematically investigated via sole and binary systems, sorption isotherm and adsorption kinetics models. The liquid-film diffusion step might be the rate-limiting step for tetracycline, the interaction of Cu(II) was more likely controlled by both intra particle diffusion model and liquid film diffusion model. The fitting of experimental data with kinetic models, Temkin model indicates that the adsorption process of tetracycline and Cu(II) involve chemisorption, and physico-chemical adsorption, respectively. There exists site competition and enhancement of Cu(II) and tetracycline on the sorption to Fe/Zn-biochar. The results of this study indicate that modification of biochar derived from sawdust shows great potential for simultaneous removal of Cu(II) and tetracycline from co-contaminated water.

Adsorption of phosphate from aqueous solution using iron-zirconium modified activated carbon nanofiber: Performance and mechanism

Phosphate (P) removal is significant for the prevention of eutrophication in natural waters. In this paper, a novel adsorbent for the removal of P from aqueous solution was synthesized by loading zirconium oxide and iron oxide onto activated carbon nanofiber (ACF-ZrFe) simultaneously. The adsorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that P adsorption was highly pH dependent and the optimum pH was found to be 4.0. The isotherm of adsorption could be well described by the Langmuir model and the maximum P adsorption capacity was estimated to be 26.3mgP/g at 25°C. The kinetic data were well fitted to the pseudo-second-order equation, indicating that chemical sorption was the rate-limiting step. Moreover, co-existing ions including sulfate (SO42-), chloride (Cl-), nitrate (NO3-) and fluoride (F-) exhibited a distinct effect on P adsorption with the order of F->NO3->Cl->SO42-. Further investigations by FT-IR spectroscopy and pH variations associated with the adsorption process revealed that ligands exchange and electrostatic interactions were the dominant mechanisms for P adsorption. The findings reported in this work highlight the potential of using ACF-ZrFe as an effective adsorbent for the removal of P in natural waters.

Treatment of arsenic in acid wastewater and river sediment by Fe@Fe2O3 nanobunches: The effect of environmental conditions and reaction mechanism

High concentration of arsenic in acid wastewater and polluted river sediment caused by metallurgical industry has presented a great environmental challenge for decades. Nanoscale zero valent iron (nZVI) can detoxify arsenic-bearing wastewater and groundwater, but the low adsorption capacity and rapid passivation restrict its large-scale application. This study proposed a highly efficient arsenic treatment nanotechnology, using the core-shell Fe@Fe2O3 nanobunches (NBZI) for removal of arsenic in acid wastewater with cyclic stability and transformation of arsenic speciation in sediment. The adsorption capacity of As(III) by NBZI was 60 times as high as that of nanoscale zero valent iron (nZVI) at neutral pH. Characterization of the prepared materials after reaction revealed that the contents of As(III) and As(V) were 65% and 35% under aerobic conditions, respectively, which is the evidence of oxidation included in the reaction process apart from adsorption and co-precipitation. The presence of oxygen was proved to improve the adsorption ability of the prepared NBZI towards As(III) with the removal efficiency increasing from 68% to 92%. In order to further enhance the performance of NBZI-2 in the absence of oxygen, a new Fenton-Like system of NBZI/H2O2 to remove arsenic under the anoxic condition was also proposed. Furthermore, the removal efficiency of arsenic in acid wastewater remained to be 78% after 9 times of cycling. Meanwhile, most of the mobile fraction of arsenic in river sediment was transformed into residues after NBZI treatment for 20 days. The reaction mechanism between NBZI and arsenic was discussed in detail at last, indicating great potential of NBZI for the treatment of arsenic in wastewater and sediment.

Solid–liquid reaction synthesis and thermalstability of Ti2SnC powders

A novel method based on the solid–liquid reaction in the Ti–Sn–C system was developed for the synthesis of Ti2SnC powders. In this process, Ti–Sn intermetallic compounds were formed in liquid Sn, then they further reacted with graphite powders to form Ti2SnC. The advantages of this solid–liquid reaction based method include low synthesis temperature, short reaction time and less impurity in the as-prepared powders. Investigations on the stability of Ti2SnC powders demonstrated that Ti2SnC was stable in Ar up to at least 1200°C. In air, however, a complex oxidation–decomposition–oxidation process was observed.

Aptamer-based biosensors for detection of lead(II) ion: a review

Lead(II) ion (Pb2+) contamination can be accumulated along the food chain and cause a serious threat to public health. Plenty of research effort has thus been devoted to the development of fast, sensitive and selective biosensors for monitoring Pb2+. Aptamer especially Pb2+ based DNAzymes (obtained from a large DNA library via in vitro selection) and DNA molecules are highly selective for a number of metal ions. Therefore, aptamer-based biosensors have been extensively studied for Pb2+ ion detection with a high sensitivity. In this review, we explain the current progress of Pb2+ aptamer-based sensors mainly in three groups: fluorescent; colorimetric; and electrochemical biosensors.

New insights into the activity of a biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions

In this work, to gain insight into the mechanism of p-nitrophenol (PNP) removal using the reactivity of a biochar supported nanoscale zerovalent iron composite (nZVI/biochar) and nanoscale zero valent iron (nZVI) under anaerobic or aerobic conditions, batch experiments and models were conducted. The PNP removal rate in the more acidic solutions was higher, while it was significantly suppressed at higher pH, especially at pH 9.0. The peak value of the apparent rate constants suggests that the reactivity of nZVI/biochar could be much stronger than that of nZVI under the same aeration conditions. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using nZVI/biochar or nZVI. The reaction constants obtained through a Langmuir–Hinshelwood mechanism under different aeration conditions followed the trend nZVI/biochar (N2) > nZVI/biochar (air) > nZVI (N2) > nZVI (air), indicating that nZVI/biochar under anaerobic conditions exhibits enhanced activity for the degradation of PNP. The nZVI/biochar under anaerobic conditions has the lowest Arrhenius activation energy of PNP degradation–adsorption, suggesting that the surface interaction of eliminating PNP has a low energy barrier. In addition, TOC removal under anaerobic conditions was negligible compared with that under the aerobic system and the total number of iron ions leaching at solution pH 3.0 in the nZVI/biochar or nZVI system under air aeration conditions was much higher than that under nitrogen aeration conditions. The profiles of the intermediates formed during the PNP degradation indicated that in the anaerobic environment, reduction was the predominant step in the removal process, while the degradation of PNP could be regarded as a combination of oxidation and reduction in an aerobic environment.

Plasmonic resonance excited dual Z-scheme BiVO4/Ag/Cu2O nanocomposite: synthesis and mechanism for enhanced photocatalytic performance in recalcitrant antibiotic degradation

The utilization of solar energy based on semiconductor photocatalysts for pollutant removal and environmental remediation has become a research hot spot and attracted great attention. In this study, a novel ternary BiVO4/Ag/Cu2O nanocomposite has been successfully synthesized via simple wet impregnation of Cu2O particles coupled with a subsequent photo-reduction pathway for the deposition of metallic Ag on the surface of BiVO4. The resulting BiVO4/Ag/Cu2O photocatalyst was used for the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). Results showed that the coating contents of the Cu2O and Ag particles presented a great effect on the eventual photocatalytic activity of the photocatalysts, and the optimum coating contents of Cu2O and Ag were obtained with their mass ratios of 3% and 2%, respectively. Under optimum conditions, nearly 91.22% TC removal efficiency was obtained based on ternary BiVO4/Ag/Cu2O nanocomposites, higher than that of pure BiVO4 (42.9%) and binary BiVO4/Cu2O (65.17%) and BiVO4/Ag (72.63%) nanocomposites. Meanwhile, the enhanced total organic carbon (TOC) removal efficiency also indicated the excellent photocatalytic degradation ability of the BiVO4/Ag/Cu2O nanocomposites. As for their practical application, the effects of initial TC concentration, various supporting electrolytes and different irradiation conditions were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs) was used to show the by-products of TC molecule degradation. Cycling experiments indicated the high stability of the as-prepared photocatalysts. Furthermore, the results obtained from radical trapping experiments and ESR measurements suggested that the photocatalytic degradation of TC in the BiVO4/Ag/Cu2O based photocatalytic system was the joint action of the photogenerated holes (h+), superoxide radical (˙O2−) and hydroxyl radical (˙OH). The enhanced photocatalytic activity of BiVO4/Ag/Cu2O was attributed to the synergistic effect of Cu2O, Ag and BiVO4, especially the surface plasmon resonance effect and the established local electric field brought about by metallic Ag. Additionally, to deeply understand the reaction mechanism, a dual Z-scheme charge transfer pathway has been proposed.

Facile fabrication of mediator-free Z-scheme photocatalyst of phosphorous-doped ultrathin graphitic carbon nitride nanosheets and bismuth vanadate composites with enhanced tetracycline degradation under visible light

To realize the sustainable employment of solar energy in contaminant degradation and environmental recovery, design and development of an efficient photocatalyst is urgently needed. Herein, a novel direct Z-scheme composite photocatalysts consist of phosphorous-doped ultrathin g-C3N4 nanosheets (PCNS) and bismuth vanadate (BiVO4) are developed via a one-pot impregnated precipitation method. The as-prepared hybrid nanocomposite was utilized for the degradation tetracycline (TC) under visible light irradiation. Among the composites with various PCNS/BiVO4 ratios, the prepared PCNS/BVO-400 photocatalyst presents the best performance, showing a TC (10mg/L) removal efficiency of 96.95% within 60min, more than double that of pristine BiVO4 (41.45%) and higher than that of pure PCNS (71.78%) under the same conditions. The effects of initial TC concentration, catalyst dosage, pH value and different water sources have been studied in detail. The improved photocatalytic performance of the as-prepared PCNS/BiVO4 nanocomposites could be attributed to the promoted separation efficiency of the photogenerated electrons and the enhanced charge carrier lifetime (1.65ns) owing to the synergistic effect between the PCNS and BiVO4. The degradation intermediates and decomposition pathway of TC were also analyzed and proposed. Additionally, radical trapping experiments and ESR measurement indicated that the photogenerated holes (h+), superoxide radical (O2-) and hydroxyl radical (OH) all participated in the TC removal procedure in the reaction system. The high performance of PCNS/BVO-400 in real wastewater indicated the potential of the prepared composite in practical application. This work provides an efficient and promising approach for the formation of high performance Z-scheme photocatalyst and study the possibility for real wastewater treatment.

Synthesis of Pd/Au bimetallic nanoparticle-loaded ultrathin graphitic carbon nitride nanosheets for highly efficientcatalytic reduction of p-nitrophenol

Noble metal nanoparticles (NPs) applied in heterogeneous catalysis have attracted considerable attention due to their highly efficient catalytic performance. Pd/Au bimetallic NPs were successfully decorated on the ultrathin graphitic carbon nitride nanosheets (g-C3N4-N) by a facile one-pot deposition reduction method. The obtained results show that Pd/Au NPs with average diameter around 8nm are homogeneously dispersed on the surface of unmodified g-C3N4-N. The obtained materials were characterized via transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). In addition, considering the large surface area and special π-bonded planar structure, the unique ultrathin g-C3N4-N behave as an excellent carrier and stabilizer in this synthesis. The as-synthesized Pd/Au bimetallic nanohybrids show superior catalytic performance and stability for reduction of p-nitrophenol (p-NP), which is better than either of pure Pd or Au nanohybrids. Besides, the catalytic activities of Pd/Au@g-C3N4-N nanohybrids were found to be controlled by altering the Pd versus Au mass ratio in the preparation process.

Metal-free carbon materials-catalyzed sulfate radical-based advanced oxidation processes: A review on heterogeneous catalysts and applications

In recent years, advanced oxidation processes (AOPs), especially sulfate radical based AOPs have been widely used in various fields of wastewater treatment due to their capability and adaptability in decontamination. Recently, metal-free carbon materials catalysts in sulfate radical production has been more and more concerned because these materials have been demonstrated to be promising alternatives to conventional metal-based catalysts, but the review of metal-free catalysts is rare. The present review outlines the current state of knowledge on the generation of sulfate radical using metal-free catalysts including carbon nanotubes, graphene, mesoporous carbon, activated carbon, activated carbon fiber, nanodiamond. The mechanism such as the radical pathway and non-radical pathway, and factors influencing of the activation of sulfate radical was also be revealed. Knowledge gaps and research needs have been identified, which include the perspectives on challenges related to metal-free catalyst, heterogeneous metal-free catalyst/persulfate systems and their potential in practical environmental remediation.