Sulfur/zinc co-doped biochar for stabilization remediation of mercury-contaminated soil: Performance, mechanism and ecological risk.

In this study, a novel sulfur/zinc co-doped biochar (SZ-BC) stabilizer was successfully developed for the remediation of mercury-contaminated soil. Results from SEM, TEM, FTIR and XRD revealed that biochar (BC) was successfully modified by sulfur and zinc. In the batch adsorption experiments, the sulfur-zinc co-pyrolysis biochar displayed excellent Hg(II) adsorption performance, with the maximum adsorption capacity of SZ-BC (261.074 mg/g) being approximately 16.5 times that of BC (15.855 mg/g). Laboratory-scale static incubation, column leaching, and plant pot experiments were conducted using biochar-based materials. At an additional dosage of 5 % mass ratio, the SZ-BC exhibits the most effective stabilization of mercury in soil, leading to a significant reduction in leaching loss compared to the control group (CK) by 51.30 %. Following 4 weeks of incubation and 2 weeks of leaching with SZ-BC, the residual mercury in the soil increased by 27.84 %. As a result, potential ecological risk index of mercury decreased by 92 % compared to the CK group. In the pot experiment, SZ-BC significantly enhanced the growth of Chinese cabbage, with biomass and root dry weight reaching 3.20 and 2.80 times that of the CK group, respectively. Additionally, the Translocation Factor (TF) and Bioconcentration Factor (BF) were reduced by 44.86 % and 74.43 %, respectively, in the SZ-BC group compared to the CK group. Moreover, SZ-BC can effectively improve enzyme activities and increase microbial communities in mercury-contaminated soils. The mechanisms of adsorption and stabilization were elucidated through electrostatic adsorption, ion exchange, surface complexation, and precipitation. These findings provide a potentially effective material for stabilizing soils contaminated with mercury.

Phosphorus-modified biochar cross-linked Mg-Al layered double-hydroxide stabilizer reduced U and Pb uptake by Indian mustard (Brassica juncea L.) in uranium contaminated soil.

The decommissioning of uranium tailings (UMT) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological security. Therefore, the remediation of uranium pollution in soil is imminent from ecological and environmental points of view. In recent years, the use of biochar stabilizers to repair uranium tailings (UMT) soil has become a research hotspot. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg-Al layered double-hydroxide composite (PBC@LDH) was prepared. The hyperaccumulator plant Indian mustard (Brassica juncea L.) was selected as the test plant for outdoor pot experiments, and the stabilizers were added to the UMT soil at the dosage ratio of 15 g kg-1, which verified the bioconcentrate and translocate of U and associated heavy metal Pb in the UMT soil by Indian mustard after stabilizer remediated. The results shown that, after 50 days of growth, compared with the untreated sample (CK), the Indian mustard in PBC@LDH treatment possessed a better growth and its biomass weight of whole plant was increased by 52.7%. Meanwhile, the bioconcentration factors (BF) of U and Pb for PBC@LDH treatment were significantly decreased by 73.4% and 34.2%, respectively; and the translocation factors (TF) were also commendable reduced by 15.1% and 2.4%, respectively. Furthermore, the Tessier available forms of U and Pb in rhizosphere soil showed a remarkably decrease compared with CK, which reached by 55.97% and 14.1% after PBC@LDH stabilization, respectively. Complexation, precipitation, and reduction of functional groups released by PBC@LDH with U and Pb described the immobilization mechanisms of biochar stabilizer preventing U and Pb enrichment in Indian mustard. As well as, the formation of U-containing vesicles was prevented by the precipitation of -OH functional groups with free U and Pb ions around the cell tissue fluids and vascular bundle structure of plant roots, thereby reducing the migration risk of toxic heavy metals to above-ground parts. In conclusion, this research demonstrates that the PBC@LDH stabilizer offers a potentially effective amendment for the remediation of U contaminated soil.

Photodegradation of E2 in the presence of natural montmorillonite and the iron complexing agent ethylenediamine-N,N'-disuccinic acid.

In this work, the photochemical degradation process of 17ß-estradiol (E2) in a suspension of natural montmorillonite (NM) has been studied. The addition of the iron complexing agent ethylenediamine-N,N'-disuccinic acid (EDDS) to the suspension was investigated and compared with the system without EDDS. The effects of the main physicochemical parameters (pH, EDDS, oxygen and NM concentrations) on E2 degradation in NM suspensions were also investigated. In order to better understand the photochemical process, experiments were carried out in the presence of 2-propanol. In general, the photochemical efficiency of the E2 degradation is better in EDDS-NM suspensions than in NM suspensions, especially at higher pH. This work demonstrated that the NM-EDDS system is an interesting and valuable research area and could be considered as a promising photochemical system for wastewater treatment.

Highly efficient photocatalytic oxidation of antibiotic ciprofloxacin using TiO2@g-C3N4@biochar composite.

In this present study, a novel indirect Z-scheme TiO2@g-C3N4@biochar (TiO2@g-C3N4@BC) composite photocatalyst was successfully fabricated and characterized with SEM, TEM, EDS, XRD, FTIR, PL, XPS, and UV-vis DRS. The photocatalytic degradation behavior of ciprofloxacin (CIP) on the TiO2@g-C3N4@BC was evaluated under UV-vis and visible light irradiation, and the possible reaction mechanism of photocatalytic oxidation of CIP on the TiO2@g-C3N4@BC was explained. The TiO2@g-C3N4@BC composite photocatalyst exhibited stronger photocatalytic oxidation activity for CIP in comparison with TiO2, g-C3N4, TiO2@BC, and TiO2@g-C3N4. After 60 min of UV-vis and visible light irradiation, the photocatalytic removal efficiency of CIP by TiO2@g-C3N4@BC was 99.3 and 89.2%, respectively. The photocatalytic removal performance of CIP was affected by the initial concentration of CIP, catalyst dosage, and pH value. The composite photocatalyst presented excellent stability and reusability after five cycles. An indirect Z-scheme principle of the CIP photocatalytic oxidation reaction on TiO2@g-C3N4@BC was clearly proposed, and the whole process of photocatalytic degradation was the results of the interaction between CIP and reactive active species (·O2-, h+, and ·OH), of which ·O2- is the main active substance. Four CIP degradation pathways were proposed. This work may provide an effective strategy to remove antibiotics in wastewater.

Intermediates in photochemistry of Fe(III) complexes with carboxylic acids in aqueous solutions.

The primary processes in the photochemistry of Fe(III) complexes with carboxylic acids (glyoxalic, tartaric, pyruvic and lactic) were studied by means of laser flash photolysis. The inner-sphere electron transfer with the formation of Fe(II) complex and an escape of an organic radical to the solution bulk was shown to be a minor channel of the photolysis. The main channel was proposed to be the formation of a long-lived radical complex [Fe(II)···Ë™OOC-R](2+). Spectral and kinetic parameters of the radical complexes are determined.

Enhanced phytoremediation of uranium-contaminated soils by Indian mustard (Brassica juncea L.) using slow release citric acid.

In this study, a novel slow release carrier for the controlled release of citric acid (CA), hydroxypropyl chitosan-graft-carboxymethyl-ß-cyclodextrin (HPCS-g-CMCD) was synthesized by the grafting reaction of carboxymethyl-ß-cyclodextrin (CMCD) with hydroxypropyl chitosan (HPCS), and the structural characteristics of HPCS-g-CMCD were confirmed by FT-IR, TGA, and NMR. Based on HPCS-g-CMCD and CA, slow release citric acid (SRCA) was prepared by a spray drying method. HPCS-g-CMCD carrier has a better slow release performance for CA compared to HPCS and CMCD, and CA release mechanism was attributed to a Fickian diffusion. Furthermore, the release behavior of uranium in contaminated soil could be effectively controlled by SRCA. The effects of SRCA on improving the phytoremediation capacity in uranium-contaminated soil were investigated using Brassica juncea, which were grown in pots containing soil with uranium at 56 mg kg-1. After 50 days of growth, 5 mmol kg-1 of CA, SRCA I, SRCA II, and SRCA III was applied, respectively. The results showed that slow release citric acid could enhance the uptake of uranium in Indian mustard. Uranium concentration in the root with SRCA I treatment was increased by 80.25% compared to the control, and the uranium removal efficiency of the SRCA I treatment was 1.66-fold greater than that of the control. Simultaneously, the leaching loss of uranium in SRCA I-treated soil was decreased by 37.35% compared to CA-treated soil. As a promising remediation strategy, SRCA-assisted phytoremediation may provide a kind of feasible technology with low leaching risk for remediation of uranium-contaminated soils.

Phosphorus-modified biochar cross-linked Mg-Al layered double-hydroxide composite for immobilizing uranium in mining contaminated soil.

The decommissioning of uranium mill tailings (UMTs) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological safety. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg-Al layered double-hydroxide (LDH) composite ("PBC@LDH") was successfully prepared by phosphate pre-impregnation and a hydrothermal method with Mg-Al LDH. Physicochemical analysis revealed that phosphorus-containing functional groups and Mg-Al LDH were grafted onto the pristine biochar (BC) matrix. Laboratory-scale incubation and column leaching experiments were performed on the prepared BC, PBC, and PBC@LDH. The results showed that, at a dosage of 10%, the PBC@LDH composite had a commendable ability to immobilize U in soil. After 40 days of incubation with the stabilizer, the more mobile U was converted into immobilized species. Furthermore, during a column leaching experiment with simulated acid rain, the cumulative loss and leaching efficiency of U were remarkably reduced by PBC@LDH treatment compared with the control, reaching 53% and 54%, respectively. Surface complexation, co-precipitation, and reduction described the adsorption and immobilization mechanisms. In conclusion, this research demonstrates that the PBC@LDH composite offers a potentially effective amendment for the remediation of U contaminated soil.

Photo-induced transformations of Hg(II) species in the presence of Nitzschia hantzschiana, ferric ion, and humic acid.

Effects of algae Nitzschia hantzschiana, Fe(III) ions, humic acid, and pH on the photochemical reduction of Hg(II) using the irradiation of metal halide lamps (lambda > or = 365 nm, 250 W) were investigated. The photoreduction rate of Hg(II) was found to increase with increasing concentrations of algae, Fe(III) ions, and humic acid. Alteration of pH value affected the photoreduction of Hg(II) in aqueous solution with or without algae. The photoreduction rate of Hg(II) decreased with increasing initial Hg(II) concentration in aqueous solution in the presence of algae. The photochemical kinetics of initial Hg(II) and algae concentrations on the photoreduction of Hg(II) were studied at pH 7.0. The study on the total Hg mass balance in terms of photochemical process revealed that more than 42% of Hg(II) from the algal suspension was reduced to volatile metallic Hg under the conditions investigated.

Adsorption of dichromate ions from aqueous solution onto magnetic graphene oxide modified by ß-cyclodextrin.

In this work, the ß-cyclodextrin modified magnetic graphene oxide (ß-CD/MGO) composite was fabricated by the in situ co-precipitation method and characterized by Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and particle size analysis. The adsorption behavior of dichromate ions on the ß-CD/MGO was investigated, and the mechanism of adsorption was also studied using FT-IR and XPS. The results from SEM and TEM showed that the graphene oxide (GO) layer became rough, and many fine particles were attached after compounding with ferroferric oxide and ß-cyclodextrin. The characterization results of FT-IR and XPS show that that ß-cyclodextrin and ferroferric oxide have been perfectly compounded to the graphene oxide layer and ß-CD/MGO has a particle size of about 460 nm, a specific surface area of 252.3 m2g-1, and a saturation magnetization of 73.5 emu g-1. The adsorption amount of dichromate ions on the ß-CD/MGO is affected by pH, adsorbent dosage, and adsorption time. Kinetic studies showed that the adsorption process followed a pseudo-second-order kinetic model. Equilibrium data agreed very well with the Langmuir model, the maximum adsorption amount of dichromate ions on the ß-CD/MGO was 49.95 mg g-1. After five successive adsorbent reuses, the reuse rate is still 73%, indicating the excellent potential reusability of ß-CD/MGO adsorbent. ß-CD/MGO exhibits excellent adsorption performance for dichromate ions. As an environmentally friendly magnetic adsorbent, ß-CD/MGO is suitable for the treatment of dichromate-containing wastewater.

Enhanced photocatalytic New Coccine degradation and Pb(II) reduction over graphene oxide-TiO2 composite in the presence of aspartic acid-ß-cyclodextrin.

In this work, aspartic acid-ß-cyclodextrin (ACD) was synthesized by the reaction of ß-cyclodextrin with aspartic acid and epichlorohydrin, and graphene oxide-TiO2 (GO-TiO2) composite catalyst was prepared by a hydrothermal method. The complexation of ACD with New Coccine (NC) and Pb2+ was characterized with FT-IR and XPS, respectively, the results show that ACD can simultaneously complex NC and Pb2+. XRD analysis and SEM images of GO-TiO2 show that TiO2 platelets are well distributed on both sides of the graphene oxide sheets, and display a similar XRD pattern to the pure TiO2 nanoparticles with the typical diffraction peak of anatase phase. The effects of ACD on the photocatalytic degradation of NC and photocatalytic reduction of Pb2+ were investigated in the single pollution system, and the synergistic effects on the simultaneous photocatalytic NC degradation and Pb2+ reduction in the presence of ACD were also evaluated. The results showed that the presence of ACD was favorable to the acceleration of photocatalytic oxidation of NC and photocatalytic reduction of Pb2+ in the single pollution system, and the photocatalytic reaction rate constants of NC and Pb2+ in the presence of ACD increased 58% and 42%, respectively. For the combined pollution system, the synergistic effects on the simultaneous conversion of NC and Pb2+ in aqueous solutions were also further enhanced. ACD enhanced photocatalytic activity was attributed to the improvement of the electron transfer and mass transfer at the GO-TiO2 interface.

Photoreduction of mercury(II) in the presence of algae, Anabaena cylindrical.

The photochemical and biological reduction of Hg(II) in the presence of algae, anabaena cylindrical, was investigated under the irradiation of metal halide lamps placed in cooling trap for maintaining constant temperature by water circulation (lambda >or=365 nm, 250 W). The photoreduction rate of Hg(II) increased with increasing algae concentration. The addition of Fe(III) and humic substances into the suspensions of algae also enhanced the photoreduction of Hg(II). Alteration of pH value affected the photoreduction of Hg(II) in aqueous solution with or without the addition of algae. The concentration of dissolved gaseous mercury (DGM), the reduced product of Hg(II), increased with increasing exposure time and then gradually approached to a steady state. The influence of initial Hg(II) concentration on the photoreduction of Hg(II) with algae was studied by irradiating the suspensions of anabaena cylindrical at pH 7.0 with initial concentrations (C(0)) of Hg(II) at 50, 100, 120, 150 and 180 microg L(-1), respectively, the light-induced reduction of Hg(II) followed the apparent pseudo first-order kinetics. The initial photoreduction rate could be expressed by the equation: r(A)=0.0871+0.00129 C(0), with a correlation coefficient R=0.9994. The overall mercury mass balance study on the photo-reductive process revealed that more than 39.86% of Hg(II) from the algal suspension was reduced to volatile metallic mercury.

Photochemical formation of hydroxyl radicals catalyzed by montmorillonite.

In this work, the photooxidation of benzene and the formation of phenol in aqueous suspensions of the iron-rich montmorillonite under irradiation of a 250W metal halide lamp (lambda> or = 365nm) were investigated. We confirmed that hydroxyl radicals (()OH) were produced by illuminating montmorillonite and was responsible for the photooxidation of benzene in aqueous suspensions of montmorillonite. Low pH value facilitated the formation of hydroxyl radicals in the pH range of 2.0-10.0. The ()OH concentration increased with increasing the concentration of montmorillonite in aqueous solutions in the range of 0-20.0gl(-1). Higher concentration like 25.0gl(-1) montmorillonite inhibited the ()OH production. Iron, predominantly free iron in the clays, is believed to be one of the most important factors determining ()OH formation. Structural irons in montmorillonite have contributions to ()OH formation, especially in the presence of carboxylate ions. The formation of ()OH from montmorillonite under irradiation of near UV and visible light indicates that clays might play important role not only in transfer through adsorption but also in transformation through oxidation of organic compounds on the surface of clay particles in air, water, soil or even top sediments.

Photodegradation of acetaminophen in TiO(2) suspended solution.

This study investigated the photocatalytic degradation of acetaminophen (APAP) in TiO(2) suspended solution under a 250 W metal halide lamp. The influence of some parameters on the degradation of acetaminophen was studied and described in details, such as initial APAP concentration, initial pH value and TiO(2) dosage. After 100 min irradiation, about 95% of APAP is decomposed in the 1.0 g L(-1) TiO(2) aqueous solution with an initial concentration of 100 micromol L(-1). The effect of adsorption at three different pH values has also been analyzed and it has been conducted that pH 3.5, at which APAP was readily adsorbed also degraded at a faster rate. Reaction rate at pH 6.9 and pH 9.5 was 2.84 and 2.96 microM min(-1), respectively. Direct hole (h(+)) oxidation and ipso-substitution was found to be the main initial step for APAP degradation. Main reaction intermediates and products were identified by GC/MS analysis. The mechanism of acetaminophen photocatalytic degradation in TiO(2) suspended solution was studied not only experimentally but also theoretically by calculating the frontier electron density of APAP. The results obtained indicated that TiO(2) photocatalytic degradation is a highly effective way to remove APAP from wastewater and drinking water without any generation of more toxic products.

Photodegradation of aniline in aqueous suspensions of microalgae.

The photodegradation of aniline was investigated using freshwater algae suspended in aqueous media under metal halide light (250 W). Four algal species were used: Nitzschia hantzschiana, Chlorella vulgaris, Chlamydomonas sajao and Anabaena cylindrica. Reactions were carried out under aerobic conditions. The photodegradation rate of aniline was accelerated by the algae. In the A. cylindrica suspensions, with cell density ranging from 2.5 x 10(5) cells mL(-1) to 6.5 x 10(6) cells mL(-1), the photodegradation rate of aniline was increased from 10% to 80% and rate constant k increased from 1.86 x 10(-3) min(-1) to 9.66 x 10(-3) min(-1). Reactive oxygen species were thought to be the main reason for the degradation of aniline. Hydroxyl radicals and singlet oxygen photogenerated in the algal suspensions were detected. The maximum singlet oxygen yield was 75 microM in the presence of 1.0 x 10(6) cells mL(-1)C. sajao. About 5 microM hydroxyl radicals were generated in the 4-h reaction. Oxygen played an important role in the formation of reactive oxygen species in the algal suspensions. The nature of the algae facilitating the photodegradation of aniline was also investigated.

Photodegradation of bisphenol Z by UV irradiation in the presence of beta-cyclodextrin.

In this work, the formation of the inclusion complex of bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane, abbreviated as BPCH) with beta-cyclodextrin (beta-CD) has been studied, 1:1 inclusion complex can be obtained, the formation constant of the beta-CD/BPCH complex is 5.94x10(3)M(-1). The photodegradation behavior of BPCH was investigated under monochromatic UV irradiation (lambda=254 nm). The photodegradation rate constant of BPCH in aqueous solutions with beta-CD showed a 9.0-fold increase, and simultaneously the mineralization of BPCH can be enhanced by beta-CD. The influence factors on photodegradation of BPCH were also studied and described in details, such as concentration of beta-CD, initial concentration of BPCH, organic solvent and pH. The photodegradation of BPCH in the presence of beta-CD includes the direct photolysis and the photooxidation of BPCH during the photochemical process. Some predominant photodegradation products are 4-(2,4,5-trihydroxy-phenyl)-4-(4-hydroxyphenyl) butanoic acid, 5,5-bis(4-hydroxyphenyl)pentanoic acid, meta-hydroxylated BPCH, ortho-hydroxylated BPCH and 4-(1-(4-hydroxyphenyl)pentyl)phenol respectively. The enhancement of photodegradation of BPCH mainly results from moderate inclusion depth of BPCH molecule in the beta-CD cavity. This kind of inclusion structure allows BPCH molecule sufficient proximity to secondary hydroxyl groups of the beta-CD cavity, and these hydroxyl groups could be activated and converted to hydroxyl radicals under UV irradiation, which can enhance the photooxidation of BPCH.

Simultaneous photocatalytic reduction of Cr(VI) and oxidation of bisphenol A induced by Fe(III)-OH complexes in water.

Simultaneously photocatalytic reduction of Cr(VI) and oxidation of bisphenol A (BPA) in aqueous solution in the presence of Fe(III)-OH complexes were investigated under a 250 W metal halide lamp (lambda>or=365 nm). Synergy effect of the simultaneous photocatalytic oxidation and reduction of both pollutants was achieved. The effects of initial pH value, initial concentration of BPA, Cr(VI) and Fe(III) were preliminarily investigated. The results showed that both photocatalytic reduction of Cr(VI) and degradation of BPA could occur simultaneously in the Fe(III)/Cr(VI)/BPA ternary system, and the rates of photocatalytic reduction of Cr(VI) and the oxidation of BPA were more rapid at a low pH range of 2.0-3.0. The increase of the initial concentration of Fe(III) was favorable to both photocatalytic reduction of Cr(VI) and oxidation of BPA. The reduction efficiency of Cr(VI) decreased with increasing initial concentrations of Cr(VI) and BPA, but the degradation efficiency of BPA was not changed obviously at different Cr(VI) concentrations.

Photodegradation of glyphosate in the ferrioxalate system.

The photoinduced degradation of glyphosate (GLP) in the ferrioxalate system was investigated under irradiation with a 250W metal halide lamp (lambda>/=365nm). The efficiency of orthophosphates release, representing the photodegradation efficiency of GLP, increased with decreasing the initial concentrations of GLP and Fe(III)/oxalate ratios. At acidic pH value in the range of 3.5-5.0, higher efficiency of orthophosphates release up to 60.6% was achieved, while the efficiency dropped to 42.1% at pH 6.0. The photochemical process mainly involved the predominant species of iron(III), namely Fe(C(2)O(4))(2)(-) and Fe(C(2)O(4))(3)(3-), which lead to the formation of hydroxyl radicals in the presence of dissolved oxygen under UV-vis irradiation. Also, the complexation of GLP with Fe(III) obviously increased the light absorption of GLP and facilitated its degradation by direct photolysis. The ninhydrin test for primary amines showed that the GLP was attacked by hydroxyl radicals with CN cleavage to yield aminomethylphosphonic acid (AMPA) and CP cleavage to yield sarcosine. The photodegradation may be enhanced by the decomposition of reactive radicals produced through ligand-to-metal charge transfer (LMCT) of ferric-GLP complexes.

Photodegradation of bisphenol A in simulated lake water containing algae, humic acid and ferric ions.

The photodegradation of bisphenol A (BPA), a suspected endocrine disruptor (ED), in simulated lake water containing algae, humic acid and Fe3+ ions was investigated. Algae, humic acid and Fe3+ ions enhanced the photodegradation of BPA. Photodegradation efficiency of BPA was 36% after 4h irradiation in the presence of 6.5 x 10(9) cells L(-1) raw Chlorella vulgaris, 4 mg L(-1) humic acid and 20 micromol L(-1) Fe3+. The photodegradation efficiency of BPA was higher in the presence of algae treated with ultrasonic than that without ultrasonic. The photodegradation efficiency of BPA in the water only containing algae treated with ultrasonic was 37% after 4h irradiation. The algae treated with heating can also enhance the photodegradation of BPA. This work helps environmental scientists to understand the photochemical behavior of BPA in lake water.

Photo-oxidation of Sb(III) in the seawater by marine phytoplankton-transition metals-light system.

The photo-oxidation of Sb(III) to Sb(V) by marine microalgae (diatom, green and red algae) with or without the presence of transition metals (Fe(III), Cu(II) and Mn(II)). The influence of marine phytoplankton on the photochemistry of antimony was confirmed for the first time. The conversion ratio of Sb(III) to Sb(V) increased with increasing algae concentration and irradiation time. Different species of marine phytoplankton were found to have different photo-oxidizing abilities. The photochemical redox of transition metals could induce the species transformation of antimony. After photo-induced oxidation by marine phytoplankton and transition metals, the ratio of Sb(V) to Sb(III) was in the range of 1.07-5.48 for six algae (Tetraselmis levis, Chlorella autotrophica, Nannochloropsis sp., Tetraselmis subcordiformis, Phaeodactylum tricornutum, and Porphyridium purpureum), and only 0.92 for Dunaliella salina. The distribution of antimony in the sunlit surface seawater was greatly affected by combined effects of marine phytoplankton (main contributor) and transition metals; both synergistic and antagonistic effects were observed. The results provided further insights into the distribution of Sb(III) and Sb(V) and the biogeochemical cycle of antimony, and have significant implications for the risk assessment of antimony in the sunlit surface seawater.

Photoreduction of chromium(VI) in the presence of algae, Chlorella vulgaris.

In this thesis, the photochemical reduction of hexavalent chromium Cr(VI) in the presence of algae, Chlorella vulgaris, was investigated under the irradiation of metal halide lamps (lambda = 365 nm, 250 W). The affecting factors of photochemical reduction were studied in detail, such as exposure time, initial Cr(VI) concentration, initial algae concentration and pH. The rate of Cr(VI) photochemical reduction increased with algae concentration increasing, exposure time increasing, initial Cr(VI) concentration decreasing and the decrease of pH. When pH increased to 6, the rate of Cr(VI) photochemical reduction nearly vanished. When initial Cr(VI) concentration ranged from 0.4 to 1.0 mg L(-1) and initial algae concentration ranged from ABS(algae) (the absorbency of algae) = 0.025 to ABS(algae) = 0.180, According to the results of kinetic analyses, the kinetic equation of Cr(VI) photochemical reduction in aqueous solution with algae under 250 W metal halide lamps was V0 = kC(0)(0.1718)A(algae)(0.5235) (C0 was initial concentration of Cr(VI); A(algae) was initial concentration of algae) under the condition of pH 4.