Nb2O5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(VI)

Niobium oxide nanowire-deposited carbon fiber (CF) samples were prepared using a hydrothermal method with amorphous Nb₂O₅·nH₂O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), UV–visible spectroscopy (UV–vis), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr(VI) was determined. Parameters such as pH value and initial Cr(VI) concentration could influence the Cr(VI) removal efficiency or adsorption capacity of the Nb₂O₅/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14 hr. The maximal Cr(VI) adsorption capacity of the Nb₂O₅ nanowire/CF sample was 115 mg/g. This Nb₂O₅/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr(VI) under UV-light irradiation: the Cr(VI) removal efficiency reached 99.9% after UV-light irradiation for 1 hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr(VI) adsorption capacity and photocatalytic performance was related to its high surface area, abundant surface hydroxyl groups, and good UV-light absorption ability.     

Performance and mechanism of Cr(VI) removal by zero-valent iron loaded onto expanded graphite

Zero-valent iron (ZVI) was loaded on expanded graphite (EG) to produce a composite material (EG-ZVI) for efficient removal of hexavalent chromium (Cr(VI)). EG and EG-ZVI were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. EG-ZVI had a high specific surface area and contained sub-micron sized particles of zero-valent iron. Batch experiments were employed to evaluate the Cr(VI) removal performance. The results showed that the Cr(VI) removal rate was 98.80% for EG-ZVI, which was higher than that for both EG (10.00%) and ZVI (29.80%). Furthermore, the removal rate of Cr(VI) by EG-ZVI showed little dependence on solution pH within a pH range of 1–9. Even at pH 11, a Cr(VI) removal rate of 62.44% was obtained after reaction for 1 hr. EG-ZVI could enhance the removal of Cr(VI) via chemical reduction and physical adsorption, respectively. X-ray photoelectron spectroscopy (XPS) was used to analyze the mechanisms of Cr(VI) removal, which indicated that the ZVI loaded on the surface was oxidized, and the removed Cr(VI) was immobilized via the formation of Cr(III) hydroxide and Cr(III)–Fe(III) hydroxide/oxyhydroxide on the surface of EG-ZVI.     

Preparation, characterization and performance of an electrospun carbon nanofiber mat applied in hexavalent chromium removal from aqueous solution

Hexavalent chromium, Cr(VI), a highly toxic oxyanion known as a carcinogen and mutagen,is an issue of concern due to its adverse impact on human health. Therefore, development of effective technologies and/or materials for Cr(VI) removal from water has been of great interest for researchers. In this study, an electrospun carbon nanofiber(CNF) mat was prepared via electrospinning polyacrylonitrile(PAN), followed by thermal pre-oxidation and carbonization. Scanning electron microscopy(SEM) observation showed that the fiber diameter of the CNF with carbonization temperature of 950°C(CNF_(950)) was about 266 nm.Potentiometric titration analysis demonstrated that the point of zero charge p H(pHpzc) of CNF_(950) was around 7.93. CNF_(950) demonstrated high adsorption capacity and fast adsorption kinetics for Cr(VI) at pH 3. Langmuir isotherm calculations showed that the maximum adsorption capacity of Cr(VI) on CNF_(950) was 118.8 mg/g at pH 2. The adsorption isotherm of Cr(VI) on CNF_(950) was well described by the Redlich–Peterson model, revealing that Cr(VI)adsorption was the result of a combination of monolayer and multilayer adsorption,depending on the initial Cr(VI) concentration. Solution pH greatly affected Cr(VI) adsorption onto CNF_(950) due to the electrostatic interaction, and the adsorption capacity was relatively high when pH was below 3. X-ray photoelectron spectroscopy(XPS) analysis revealed that the removal of Cr(VI) might be the result of a combination of redox reaction and electrostatic adsorption. The adsorption-saturated CNF_(950) could be regenerated by NaOH solution. This study extends the potential applicability of electrospun CNF mats for Cr(VI)-contaminated water purification.     

Investigation of adsorption/desorption behavior of Cr(VI) at the presence of inorganic and organic substance in membrane capacitive deionization (MCDI)

The adsorption and desorption behavior of Cr(VI) in membrane capacitive deionization (MCDI) was investigated systematically in the presence of bovine serum albumin (BSA) and KCl with different concentrations, respectively. Results revealed that Cr(VI) absorption was enhanced and the adsorption amount for Cr(VI) increased from 155.7 to 190.8?mg/g when KCl concentration increased from 100 to 200?mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2?mg/g when KCl concentration reached up to 1000?mg/L suggesting the negative effect for Cr(VI) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr (VI) significantly declined to 78.3?mg/g and pH was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(VI) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy (EDS). Based on above analysis, the enhanced removal mechanism for Cr(VI) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(VI) into Cr(III) and precipitation, which was demonstrated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).     

Performance and mechanism of Cr(Ⅵ) removal by zero-valent iron loaded onto expanded graphite

Zero-valent iron(ZⅥ) was loaded on expanded graphite(EG) to produce a composite material(EG-ZⅥ) for efficient removal of hexavalent chromium(Cr(Ⅵ)). EG and EG-ZⅥ were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM),Fourier-transform infrared(FTIR) spectroscopy and Brunauer–Emmett–Teller(BET) analysis. EG-ZⅥ had a high specific surface area and contained sub-micron sized particles of zero-valent iron. Batch experiments were employed to evaluate the Cr(Ⅵ) removal performance. The results showed that the Cr(Ⅵ) removal rate was 98.80% for EG-ZⅥ,which was higher than that for both EG(10.00%) and ZⅥ(29.80%). Furthermore, the removal rate of Cr(Ⅵ) by EG-ZⅥ showed little dependence on solution p H within a p H range of 1–9.Even at pH 11, a Cr(Ⅵ) removal rate of 62.44% was obtained after reaction for 1 hr. EG-ZⅥ could enhance the removal of Cr(Ⅵ) via chemical reduction and physical adsorption,respectively. X-ray photoelectron spectroscopy(XPS) was used to analyze the mechanisms of Cr(Ⅵ) removal, which indicated that the ZⅥ loaded on the surface was oxidized, and the removed Cr(Ⅵ) was immobilized via the formation of Cr(III) hydroxide and Cr(III)–Fe(III)hydroxide/oxyhydroxide on the surface of EG-ZⅥ.     

Novel functional fiber loaded with carbon dots for the deep removal of Cr(VI) by adsorption and photocatalytic reduction

A novel functional fiber (PAN-CDs) loaded with carbon dots (CDs) with excellent photoreduction and adsorption properties for Cr(VI) was prepared via an amidization reaction between the CDs' carboxyl groups and amine groups on polyacrylonitrile (PAN)-based ion exchange fibers, which could completely preserve the fluorescence properties of the CDs. The photoluminescence (PL), photocatalysis and adsorption properties of PAN-CDs were characterized and analyzed. The PAN-CDs possess high adsorption capacity (297.6?mg/g) and excellent kinetic behavior (attaining adsorption equilibrium in 30?min) for Cr(VI) adsorption. Furthermore, the residual Cr(VI) (approximately 3?mg/L) after adsorption could be removed completely by subsequent photoreduction by the PAN-CDs. The Cr-saturated PAN-CDs could be easily separated by filtering and regenerated, with no observable decay of removal efficiency after five regeneration cycles. In addition, due to the PL quenching action of Cr(VI), the PAN-CDs can also be used as sensor for quantitative detection of trace Cr(VI) in aqueous solution.     

Simultaneous removal of Cu(Ⅱ) and Cr(Ⅵ) by Mg–Al–Cl layered double hydroxide and mechanism insight

Mg–Al–Cl layered double hydroxide(Cl-LDH) was prepared to simultaneously remove Cu(Ⅱ)and Cr(VI) from aqueous solution. The coexisting Cu(Ⅱ)(20 mg/L) and Cr(VI)(40 mg/L) were completely removed within 30 min by Cl-LDH in a dosage of 2.0 g/L; the removal rate of Cu(Ⅱ) was accelerated in the presence of Cr(VI). Moreover, compared with the adsorption of single Cu(Ⅱ) or Cr(VI), the adsorption capacities of Cl-LDH for Cu(Ⅱ) and Cr(VI) can be improved by 81.05% and 49.56%, respectively, in the case of coexisting Cu(Ⅱ)(200 mg/L) and Cr(VI)(400 mg/L). The affecting factors(such as solution initial p H, adsorbent dosage, and contact time) have been systematically investigated. Besides, the changes of p H values and the concentrations of Mg~(2+) and Al~(2+)in relevant solutions were monitored. To get the underlying mechanism, the Cl-LDH samples before and after adsorption were thoroughly characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. On the basis of these analyses, a possible mechanism was proposed. The coadsorption process involves anion exchange of Cr(VI) with Cl-in Cl-LDH interlayer, isomorphic substitution of Mg~(2+) with Cu~(2+), formation of Cu_2Cl(OH)_3precipitation, and the adsorption of Cr(VI) by Cu_2Cl(OH)_3. This work provides a new insight into simultaneous removal of heavy metal cations and anions from wastewater by Cl-LDH.     

Preparation and photocatalytic properties of porous C and N co-doped TiO2 deposited on brick by a fast, one-step microwave irradiation method

A one-step microwave irradiation method was used to deposit carbon and nitrogen co-doped TiO_2((C, N)-TiO_2) on commercial brick((C, N)-TiO_2/brick). The as-prepared samples were characterized by X-ray diffraction, ultraviolet–visible(UV–vis) diffuse reflectance spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy(SEM). A selective technique was also used to investigate the concentration of hydroxyl radicals during UV–vis irradiation of the Methyl Orange solution with the as-prepared samples. The C and N dopants enhanced visible light absorption and provided a longer lifetime for the photo-generated electron–hole pairs. The SEM images showed that the as-prepared sample is porous. The dark adsorption and photodegradation test for(C, N)-TiO_2/brick showed good photodegradation and good recyclability. The best photodegradation rate was 94% after 2 hr. The maximum degradation rate was maintained even after the 6th cycle. The good photocatalytic properties are attributed to the enhanced visible light absorption, enhanced pollutant adsorption arising from the porous structure of the(C, N)-TiO_2 thin film, and longer lifetime of the photo-generated electron–hole pairs.(C, N)-TiO_2/brick should have potential commercial applications in photodegradation processes because of its low cost, good photodegradation, and excellent recyclability.     

Facile synthesis of graphitic carbon-nitride supported antimony-doped tin oxide nanocomposite and its application for the adsorption of volatile organic compounds

Antimony-doped tin oxide(ATO) nanoparticles with an average size of ～ 6 nm were prepared by co-precipitation and subsequent heat treatment. Graphitic carbon nitride(g-CN)/ATO hybrid nanocomposite was designed by the combination of thermally synthesized g-CN and ATO nanoparticles by ultrasonication. The materials were characterized using N2 adsorption/desorption(BET), X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and Fourier transform infrared spectroscopy(FTIR). A mixture of five volatile organic compounds(VOCs, chloroform, benzene, toluene, xylene and styrene) was used to compare the adsorption capacity of the samples. The adsorption capacity of ATO nanoparticles was improved by the addition of g-CN. Experimental data showed that, among the five VOCs,chloroform was the least adsorbed, regardless of the samples. The g-CN/ATO showed nearly three times greater adsorption capacity for the VOC mixture than pure ATO. The unchanged efficiency of VOC adsorption during cyclic use demonstrated the completely reversible adsorption and desorption behavior of the nanocomposite at room conditions. This economically and environmentally friendly material can be a practical solution for outdoor and indoor VOC removal.     

Graphene TiO2 nanocomposites with high photocatalytic activity for the degradation of sodium pentachlorophenol

A series of graphene–TiO2photocatalysts was synthesized by doping TiO2 with graphene oxide via hydrothermal treatment. The photocatalytic capability of the catalysts under ultraviolet irradiation was evaluated in terms of sodium pentachlorophenol（PCP-Na） decomposition and mineralization. The structural and physicochemical properties of these nanocomposites were characterized by X-ray diffraction, N2adsorption–desorption, transmission electron microscopy, scanning electron microscopy, Ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectra, and Fourier-transform infrared spectroscopy. The graphene–TiO2nanocomposites exhibited higher photocatalytic efficiency than commercial P25 for the degradation of PCP-Na, and 63.4% to 82.9% of the total organic carbon was fully mineralized. The improved photocatalytic activity may be attributed to the accelerated interfacial electron-transfer process and the significantly prolonged lifetime of electron-hole pairs imparted by graphene sheets in the nanocomposites. However,excessive graphene and the inhomogeneous aggregation of TiO2 nanoparticles may decrease photodegradation efficiency.     

La/Ce-codoped Bi2O3 composite photocatalysts with high photocatalytic performance in removal of high concentration dye

A series of La/Ce-codoped Bi_2O_3 composite photocatalysts were fabricated via hydrothermal–calcination process. The as-prepared products were intensively characterized by some physicochemical characterizations like N_2 physical adsorption, X-ray powder diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), UV–Vis diffuse reflectance(UV–Vis DRS), Fourier transform infrared spectroscopy(FT-IR),photoelectrochemical measurements, and photoluminescence(PL) spectroscopy. The characterization results indicated that La and Ce doping induced obvious crystal phase transformation in Bi_2O_3, from monoclinic to tetragonal phase. La and Ce codoping also gave rise to the obvious synergetic effects, e.g., the lattice contraction of Bi_2O_3, the decrease of crystal size and the increase of surface area. The photocatalytic performance of the prepared catalysts was evaluated by removal of dye acid orange II with high concentration under visible light irradiation. Results showed that La/Ce-codoped Bi_2O_3 displayed much higher photocatalytic performance than that of bare Bi_2O_3, single La or Ce doped Bi_2O_3 samples. The superior photocatalytic activity was mainly attributed to the improved texture and surface properties and the synergistic effects of La and Ce codoping on suppressing the recombination of photo-generated electrons(e~-) and holes(h~+).     

Enhanced photocatalytic activity of rGO/TiO2 for the decomposition of formaldehyde under visible light irradiation

Due to the low concentration of indoor air contaminants,photocatalytic technology shows low efficiency for indoor air purification.The application of TiO_2 for photocatalytic removal of formaldehyde is limited,because TiO_2 can only absorb ultraviolet(UV) light.Immobilization of TiO_2 nanoparticles on the surface of graphene can improve the visible light photocatalytic activity and the adsorption capacity.In this study,rGO(reduced graphene oxide)/TiO_2 was synthesized through a hydrothermal method using titanium tetrabutoxide and graphene oxide as precursors,and was used for the degradation of low concentration formaldehyde in indoor air under visible light illumination.Characterization of the crystalline structure and morphology of rGO/TiO_2 revealed that most GO was reduced to rGO during the hydrothermal treatment,and anatase TiO_2 nanoparticles(with particle size of 15–30 nm) were dispersed well on the surface of the rGO sheets.rGO/TiO_2 exhibited excellent photocatalytic activity for degradation of formaldehyde in indoor air and this can be attributed to the role of rGO,which can act as the electron sink and transporter for separating photo-generated electron–hole pairs through interfacial charge transfer.Furthermore,rGO could adsorb formaldehyde molecules from air to produce a high concentration of formaldehyde on the surface of rGO/TiO_2.Under visible light irradiation for 240 min,the concentration of formaldehyde could be reduced to 58.5 ppbV.rGO/TiO_2 showed excellent moisture-resistance behavior,and after five cycles,r GO/TiO_2 maintained high photocatalytic activity for the removal of formaldehyde(84.6%).This work suggests that the synthesized rGO/TiO_2 is a promising photocatalyst for indoor formaldehyde removal.     

Adsorption-oxidation of hydrogen sulfide on Fe/walnut-shell activated carbon surface modified by NH3-plasma

Walnut-shell activated carbon(WSAC) supported ferric oxide was modified by non-thermal plasma(NTP), and the removal efficiency for hydrogen sulfide over Fe/WSAC modified by dielectric barrier discharge(DBD) was significantly promoted. The sample modified for10 min and 6.8 k V output(30 V input voltage) maintained 100% H2 S conversion over a long reaction time of 390 min. The surface properties of adsorbents modified by NTP under different conditions were evaluated by the methods of X-ray photoelectron spectroscopy(XPS), Brunauer–Emmett–Teller(BET) analysis and in-situ Fourier transform infrared spectroscopy(FTIR), to help understand the effect of the NTP treatment. NTP treatment enhanced the adsorption capacity of Fe/WSAC, which could due to the formation of micro-pores with sizes of0.4, 0.5 and 0.75 nm. XPS revealed that chemisorbed oxygen changed into lattice oxygen after NTP treatment, and lattice oxygen is beneficial for H2 S oxidation. From the in-situ FTIR result,transformation of the reaction path on Fe/WSAC was observed after NTP modification. The research results indicate that NTP is an effective method to improve the surface properties of the Fe/WSAC catalyst for H2 S adsorption-oxidation.     

Phosphate removal from domestic wastewater using thermally modified steel slag

This study was performed to investigate the removal of phosphate from domestic wastewater using a modified steel slag as the adsorbent. The adsorption effects of alkalinity, salt, water,and thermal modification were investigated. The results showed that thermal activation at 800℃ for 1 hr was the optimum operation to improve the adsorption capacity. The adsorption process of the thermally modified slag was well described by the Elovich kinetic model and the Langmuir isotherm model. The maximum adsorption capacity calculated from the Langmuir model reached 13.62 mg/g. Scanning electron microscopy indicated that the surface of the modified slag was cracked and that the texture became loose after heating. The surface area and pore volume did not change after thermal modification. In the treatment of domestic wastewater, the modified slag bed(35.5 kg) removed phosphate effectively and operated for 158 days until the effluent P rose above the limit concentration of 0.5 mg/L. The phosphate fractionation method, which is often applied in soil research, was used to analyze the phosphate adsorption behavior in the slag bed. The analysis revealed that the total contents of various Ca–P forms accounted for 81.4%–91.1%, i.e., Ca10–P 50.6%–65.1%, Ca8–P 17.8%–25.0%,and Ca2–P 4.66%–9.20%. The forms of Al–P, Fe–P, and O–P accounted for only 8.9%–18.6%. The formation of Ca10–P precipitates was considered to be the main mechanism of phosphate removal in the thermally modified slag bed.     

Influence of the structure and composition of Fe–Mn binary oxides on rGO on As(Ⅲ) removal from aquifers

Fe–Mn binary oxide(FMBO) possesses high efficiency for As(Ⅲ) abatement based on the good adsorption affinity of iron oxide and the oxidizing capacity of Mn(Ⅳ), and the composition and structure of FMBO play important roles in this process.To compare the removal performance and determine the optimum formula for FMBO, magnetic graphene oxide(MRGO)–FMBO and MRGO–MnO_2 were synthesized with MRGO as a carrier to improve the dispersity of the adsorbents in aquifers and achieve magnetic recycling.Results indicated that MRGO–FMBO had higher As(Ⅲ) removal than that of MRGO–MnO_2,although the ratios of Fe and Mn were similar, because the binary oxide of Fe and Mn facilitated electron transfer from Mn(Ⅳ) to As(Ⅲ), while the separation of Mn and Fe on MRGO–MnO_2 restricted the process.The optimal stoichiometry x for MRGO–FMBO(Mn_xFe_(3-x)O_4) was 0.46, and an extraordinary adsorption capacity of 24.38 mg/g for As(Ⅲ) was achieved.MRGO–FMBO showed stable dispersive properties in aquifers, and exhibited excellent practicability and reusability, with a saturation magnetization of 7.6 emu/g and high conservation of magnetic properties after 5 cycles of regeneration and reuse.In addition, the presence of coexisting ions would not restrict the practical application of MRGO–FMBO in groundwater remediation.The redox reactions of As(Ⅲ) and Mn(Ⅳ) on MRGO–FMBO were also described.The deprotonated aqueous As(Ⅲ) on the surface of MRGO–FMBO transferred electrons to Mn(Ⅳ), and the formed As(Ⅴ) oxyanions were bound to ferric oxide as inner-sphere complexes by coordinating their "–OH" groups with Mn(Ⅳ)oxides at the surface of MRGO–FMBO.This work could provide new insights into highperformance removal of As(Ⅲ) in aquifers.     

Investigation of adsorption/desorption behavior of Cr(Ⅵ) at the presence of inorganic and organic substance in membrane capacitive deionization(MCDI)

The adsorption and desorption behavior of Cr(Ⅵ) in membrane capacitive deionization(MCDI) was investigated systematically in the presence of bovine serum albumin(BSA) and KCl with different concentrations, respectively. Results revealed that Cr(Ⅵ) absorption was enhanced and the adsorption amount for Cr(Ⅵ) increased from 155.7 to 190.8 mg/g when KCl concentration increased from 100 to 200 mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2 mg/g when KCl concentration reached up to 1000 mg/L suggesting the negative effect for Cr(Ⅵ) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr(Ⅵ) significantly declined to 78.3 mg/g and p H was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(Ⅵ) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy(EDS). Based on above analysis, the enhanced removal mechanism for Cr(Ⅵ) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(Ⅵ) into Cr(III)and precipitation, which was demonstrated by X-ray photoelectron spectroscopy(XPS) and scanning electron microscope(SEM).     

Removal of heavy metals using waste eggshell

The removal capacity of toxic heavy metals by the reused eggshell was studied.As a pretreatment process for the preparation of reused material from waste eggshell,calcination was performed in the furnace at 800℃for 2 h after crushing the dried waste eggshell.Calcination behavior,qualitative and quantitative elemental information,mineral type and surface characteristics before and after calcination of eggshell were examined by thermal gravimetric analysis(TGA),X-ray fluorescence (XRF),X-ray diffraction(XRD) and scanning electron microscopy(SEM),respectively.After calcination,the major inorganic composition was identified as Ca(lime, 99.63%)and K,P and Sr were identified as minor components.When calcined eggshell was applied in the treatment of synthetic wastewater containing heavy metals,a complete removal of Cd as well as above 99% removal of Cr was observed after 10 min. Although the natural eggshell had some removal capacity of Cd and Cr,a complete removal was not accomplished even after 60 min due to quite slower removal rate.However,in contrast to Cd and Cr,an efficient removal of Pb was observed with the natural eggshell rather than the calcined eggshell.From the application of the calcined eggshell in the treatment of real electroplating wastewater, the calcined eggshell showed a promising removal capacity of heavy metal ions as well as had a good neutralization capacity in the treatment of strong acidic wastewater.     

Nanoscale zero-valent iron/magnetite carbon composites for highly efficient immobilization of U(VI)

Nanoscale zerovalent iron/magnetic carbon (NZVI/MC) composites were successfully synthesized by simply calcining yellow pine and iron precursors. NZVI/MC pyrolyzed at 800°C (NZVI/MC800) had a higher percentage of NZVI and displayed better resistance to aggregation and oxidation of NZVI than samples prepared at other temperatures. The NZVI/MC800 material was applied for the elimination of U(VI) from aqueous solutions. The results suggested that the NZVI/MC800 displayed excellent adsorption capacity (203.94?mg/g) toward U(VI). The significant adsorption capacity and fast adsorption kinetics were attributed to the presence of well-dispersed NZVI, which could quickly reduce U(VI) into U(IV), trapping the guest U(IV) in the porous biocarbon matrix. The removal of U(VI) on the NZVI/MC samples was strongly affected by solution pH. The NZVI/MC samples also displayed outstanding reusability for U(VI) removal after multiple cycles. These findings indicate that NZVI/MC has great potential for remediation of wastewater containing U(VI).     

Integrated removal of NO and mercury from coal combustion flue gas using manganese oxides supported on TiO2

A catalyst composed of manganese oxides supported on titania(MnO_x/TiO_2) synthesized by a sol–gel method was selected to remove nitric oxide and mercury jointly at a relatively low temperature in simulated flue gas from coal-fired power plants. The physico-chemical characteristics of catalysts were investigated by X-ray fluorescence(XRF), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS) analyses, etc. The effects of Mn loading,reaction temperature and individual flue gas components on denitration and Hg~0 removal were examined. The results indicated that the optimal Mn/Ti molar ratio was 0.8 and the best working temperature was 240°C for NO conversion. O_2 and a proper ratio of [NH_3]/[NO]are essential for the denitration reaction. Both NO conversion and Hg~0 removal efficiency could reach more than 80% when NO and Hg~0 were removed simultaneously using Mn0.8 Tiat 240°C.Hg~0 removal efficiency slightly declined as the Mn content increased in the catalysts. The reaction temperature had no significant effect on Hg~0 removal efficiency. O_2 and HCl had a promotional effect on Hg~0 removal. SO2 and NH_3were observed to weaken Hg~0 removal because of competitive adsorption. NO first facilitated Hg~0 removal and then had an inhibiting effect as NO concentration increased without O_2, and it exhibited weak inhibition of Hg~0 removal efficiency in the presence of O_2. The oxidation of Hg~0 on Mn O x/TiO_2 follows the Mars–Maessen and Langmuir–Hinshelwood mechanisms.     

Revealing the effect of preparation parameters on zeolite adsorption performance for low and medium concentrations of ammonium

The effect of preparation parameters on the performance of zeolite for ammonium(20–300 mg N/L) adsorption from simulated wastewater is reported. It was found that the ratios of Na_2O/SiO_2 and Si/Al had a more important influence than crystallization time on zeolite adsorption properties. Relatively low Na_2O/SiO_2 ratios were beneficial for fabrication of zeolites with high proportions of micropore area and volume, which led to the surface adsorption mechanism being dominated by surface free energy and pore effects. However,with decreasing Si/Al ratios, the effect of ion-exchange was more prominent due to the high negative surface potential of zeolite. In addition, the concentration of weak acid sites on the zeolites was increased with lower ratios of Na_2O/SiO_2 and Si/Al, which may promote ammonium removal. Therefore, the most effective zeolite for ammonium removal, which was fabricated at Na_2O/SiO_2= 1.375, Si/Al = 4 and crystallization time of 48 hr, exhibited the cooperative effects of adsorption, ion-exchange and a large amount of weak acid sites. The maximum ammonium adsorption capacity(35.06 ± 0.98 mg/g) and the removal efficiency(94.44% ± 4.00%) were obtained at the dosage of 4.0 g/L zeolite NaX at ammonium concentrations of 300 mg N/L and 20 mg N/L, respectively. The Freundlich isotherm and pseudo-first-order kinetics models provided excellent fitting for the ammonium adsorption process. In addition, zeolite NaX showed about 1.23–3.2 times the ammonium adsorption capacity of clinoptilolite. The stable and efficient reusability of zeolite NaX after five regeneration cycles demonstrated that this adsorbent has considerable potential for practical industrial applications.