Efficient Degradation of Sulfamethoxazole by Diatomite-Supported Hydroxyl-Modified UIO-66 Photocatalyst after Calcination.

Sulfamethoxazole (SMX) is a widely used antibiotic to treat bacterial infections prevalent among humans and animals. SMX undergoes several transformation pathways in living organisms and external environments. Therefore, the development of efficient remediation methods for treating SMX and its metabolites is needed. We fabricated a photo-Fenton catalyst using an UIO-66 (Zr) metal-organic framework (MOF) dispersed in diatomite by a single-step solvothermal method for hydroxylation (HO-UIO-66). The HO-UIO-66-0/DE-assisted Fenton-like process degraded SMX with 94.7% efficiency; however, HO-UIO-66 (Zr) is not stable. We improved the stability of the catalyst by introducing a calcination step. The calcination temperature is critical to improving the catalytic efficiency of the composite (for example, designated as HO-UIO-66/DE-300 to denote hydroxylated UIO-66 dispersed in diatomite calcined at 300 °C). The degradation of SMX by HO-UIO-66/DE-300 was 93.8% in 120 min with 4 mmol/L H2O2 at pH 3 under visible light radiation. The O1s XPS signatures signify the stability of the catalyst after repeated use for SMX degradation. The electron spin resonance spectral data suggest the role of h+, •OH, •O2-, and 1O2 in SMX degradation routes. The HO-UIO-66/DE-300-assisted Fenton-like process shows potential in degrading pharmaceutical products present in water and wastewater.

Fluorescence characteristics and source analysis of DOM in groundwater during the wet season in the CKDu zone of North Central Province, Sri Lanka.

The dissolved organic matter (DOM) should be purified for safe drinking water due to disinfection by-products (DBPs) produced by disinfectants reaction with DOM. Current research on groundwater in the chronic kidney disease with unknown etiology (CKDu) zone of the North Central Province (NCP) in Sri Lanka has focused mainly on aquatic chemistry, with limited attention paid to the spatial distribution, compositional sources and factors of DOM. Therefore, the structure, composition, source and spatial distribution of the DOM of two kinds of groundwater samples collected from dug well and tube well in the NCP during the wet season were determined, compared and analyzed by analytical tools such as parallel factor analysis (PARAFAC). Results show that the average concentrations of TOC in these two groundwater samples are generally higher than 5.0 mg/L, and the concentration of TOC in the groundwater of the shallow weathered aquifer is higher than that of the deep hard rock aquifer, while its distribution of the two aquifers are on contrary. The DOM in the dug well has three types and four components, including humus-like component C1 (33.36%) and C2 (38.60%), protein-like component C3 (13.09%) and heterogeneous organic component C4 (14.95%). In the tube well, two types and two components of the DOM are determined, including humus-like component CⅠ (69.80%) widely existing in natural water and soluble microbial by-product CⅡ (30.20%) produced by microbial community activities. In the dug well, DOM is mainly exogenous input, the higher ion concentration in water affected the fluorescence intensity of humus and protein components. And in the tube well, DOM has obvious endogenous characteristics, and higher pH value may inhibit the production of protein like fluorescent substances to a certain extent.

The metal-organic framework supported gold nanoparticles as a highly sensitive platform for electrochemical detection of methyl mercury species in the aqueous environment.

Mercury readily methylates to form extremely toxic methylmercury (CH3Hg+) that seriously imparts central nervous systems' functionality in humans and animals. Therefore, the development of rapid CH3Hg+ determination methods for the detection of environmentally relevant concentrations is a research priority. We developed an electrochemical technique to detect CH3Hg+ with minimal sample preparations, cost-effectively. Gold nanoparticles (AuNPs) were synthesized on metal-organic frameworks (MOFs) in a facile way using potassium borohydride as a reductant. An electrochemical sensor was developed using Au nanoparticles and zeolitic imidazolate framework-67 (Au/ZIF67) modified glassy carbon electrode (Au/ZIF67 GCE) for the determination of CH3Hg+. The linear stripping current responses were ranging from 1 µg/L to 25 µg/L [CH3Hg+], with 0.571 µA/µgL-1 sensitivity and 0.05 µg/L detection limit. The outstanding performance of Au/ZIF67 modified GCE for CH3Hg+ detection might be attributed to the unique hollow structure and active Co sites of the ZIF67 skeleton and catalytic activity of AuNPs. The new electrochemical sensor shows good stability and no interference by metal ions in the matrix. The Au/ZIF67 modified GCE sensor shows a good promise in detecting CH3Hg+ in natural water.

Magnetic recyclable heterogeneous catalyst Fe3O4/g-C3N4 for tetracycline hydrochloride degradation via photo-Fenton process under visible light.

Antibiotic pollution of water resources is a global problem, and the development of new treatments for destroying antibiotics in water is a priority research. We successfully manufactured recyclable magnetic Fe3O4/g-C3N4 through the electrostatic self-assembly method. Selecting tetracycline (TC) as the target pollutant, using Fe3O4/g-C3N4 and H2O2 developed a heterogeneous optical Fenton system to remove TC under visible light. Fe3O4/g-C3N4 was systematically characterized by SEM, TEM, XRD, FTIR, XPS, DRS, and electrochemical methods. The removal efficiency of 7% Fe3O4/g-C3N4 at pH = 3, H2O2 = 5 mM, and catalyst dosage of 1.0 g/L can reach 99.8%. After magnetic separation, the Fe3O4/g-C3N4 photocatalyst can be recycled five times with minimal efficiency loss. The excellent degradation performance of the prepared catalyst may be attributed to the proper coupling interface between Fe3O4 and g-C3N4 which promotes the separation and transfer of photogenerated electrons. Photogenerated electrons can also accelerate the conversion of Fe3+ to Fe2+, thereby producing more ˙OH. The new Fe3O4/g-C3N4 can be used as a raw material for advanced oxidation of water contaminated by refractory antibiotics.

Ambient PM2.5 and PM10 Exposure and Respiratory Disease Hospitalization in Kandy, Sri Lanka.

Evidence of associations between exposure to ambient air pollution and health outcomes are sparse in the South Asian region due to limited air pollution exposure and quality health data. This study investigated the potential impacts of ambient particulate matter (PM) on respiratory disease hospitalization in Kandy, Sri Lanka for the year 2019. The Generalized Additive Model (GAM) was applied to estimate the short-term effect of ambient PM on respiratory disease hospitalization. As the second analysis, respiratory disease hospitalizations during two distinct air pollution periods were analyzed. Each 10 µg/m3 increase in same-day exposure to PM2.5 and PM10 was associated with an increased risk of respiratory disease hospitalization by 1.95% (0.25, 3.67) and 1.63% (0.16, 3.12), respectively. The effect of PM2.5 or PM10 on asthma hospitalizations were 4.67% (1.23, 8.23) and 4.04% (1.06, 7.11), respectively (p < 0.05). The 65+ years age group had a higher risk associated with PM2.5 and PM10 exposure and hospital admissions for all respiratory diseases on the same day (2.74% and 2.28%, respectively). Compared to the lower ambient air pollution period, higher increased hospital admissions were observed among those aged above 65 years, males, and COPD and pneumonia hospital admissions during the high ambient air pollution period. Active efforts are crucial to improve ambient air quality in this region to reduce the health effects.

Evaluation of Performance of Existing RO Drinking Water Stations in the North Central Province, Sri Lanka.

Reverse osmosis (RO) drinking water stations have been introduced to provide safe drinking water for areas with prevailing chronic kidney disease with unknown (CKDu) etiology in the dry zone of Sri Lanka. In this investigation, RO drinking water stations established by community-based organizations (CBO) in the North Central Province (NCP) were examined. Water samples were collected from source, permeate, and concentrate in each station to determine water quality and performance. Furthermore, the operators of the systems were interviewed to evaluate operational and maintenance practices to identify major issues related to the RO systems. Results show that the majority (>93%) of RO systems had higher salt rejection rates (>92%), while water recovery varied from 19.4% to 64%. The removal efficiencies of hardness and alkalinity were averaged at 95.8% and 86.6%, respectively. Most dominant ions such as Ca2+, Mg2+, K+, Na+, Ba2+, Sr2+ Cl-, F-, and SO42- showed higher rejections at averaged values of 93.5%, 97.4%, 86.6%, 90.8%, 95.4%, 96.3%, 95.7%, 96.6%, and 99.0%, respectively. Low recovery rates, lower fluoride levels in product water, and membrane fouling were the main challenges. Lack of knowledge and training were the major issues that could shorten the lifespan of RO systems.

Optimized pre-treatment of high strength food waste digestate by high content aluminum-nanocluster based magnetic coagulation.

Coagulation-based pre-treatment efficiency of high strength digestate of food waste (HSDFW) anaerobic digestion is negated by organic ligand-catalyzed decomposition of coagulants. In this study, an efficient HSDFW pre-treatment method, magnetic seeds (MS) coagulation, was employed by using highly stable Keggin Al30 nanocluster (PAC30), MS and polyacrylamide (PAM), and its operation was optimized by evaluating the performance of removing turbidity, total suspended solids (TSS), chemical oxygen demand (COD), and total phosphorous (TP) phosphate. Results showed that at the optimum dosage of 4.82 g/L, PAC30 demonstrated excellent removals as high as 98.93% ± 0.1% of turbidity, 98.04% ± 0.1% of TSS, 58.28% ± 0.3% of total COD, 99.98% ± 0.01% of TP and 99.50% ± 0.01% of dissolved phosphate, respectively. Apparent molecular weight (AMW) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analyses demonstrated more efficient removal of dissolved organic matter (DOM), particularly non-biodegradable and hydrophobic components by PAC30 than commercial coagulant. The sedimentation was much improved from 40 min by coagulation/flocculation to about 5 min settling by MS coagulation. The PAC30 based magnetic coagulation (MC) presents theoretical guidance on a cost-effective and much less footprint pre-treatment alternative for high strength wastewater.

Household Air Pollution from Biomass Fuel for Cooking and Adverse Fetal Growth Outcomes in Rural Sri Lanka.

The aim of this study was to investigate the impact of biomass fuel for cooking on adverse fetal growth outcomes in Sri Lanka. A cross-sectional study of mothers recruited at maternity clinics in rural communities in Sri Lanka's Central Province was undertaken. Data pertaining to household air pollution and fetal growth parameters were collected using an interviewer-administered questionnaire. Logistic regression models, adjusted for potential confounders, were used to evaluate the impact of biomass fuel for cooking on low birth weight (LBW) and small for gestational age (SGA) parameters. Findings showed that exposure to biomass cooking fuels during pregnancy was associated with an increased risk of LBW adjusted odds ratio (aOR) 2.74 (95% CI 1.08-6.96) and SGA (aOR: 1.87, 95% CI 1.03-3.41) compared with the use of clean energy. The risk of LBW was highest for traditional biomass stoves compared to improved biomass stoves (aOR: 3.23, 95% 1.17-8.89) and biomass use in kitchens without a chimney compared to kitchens with a chimney (aOR: 4.63, 95% 1.54-13.93). Similar trends were observed for SGA.

Comparison of an integrated short-cut biological nitrogen removal process with magnetic coagulation treating swine wastewater and food waste digestate.

An integration of two processes, magnetic coagulation (MC) and short-cut biological nitrogen removal (SBNR), coupled with a sequencing batch membrane bioreactor (SMBR) controlled by an automatic real-time control strategy (RTC), was developed to treat different characteristics of high strength wastewater. The treatment efficiency and microbial community-diversity of the proposed method was evaluated and investigated using swine wastewater and food waste (FW) digestate. The MC showed high removal of TSS (89.1 ± 1.5%, 92.21 ± 1.8%), turbidity (90.58 ± 2.1%, 95.1 ± 2.1%), TP (88.5 ± 1.9%, 92.1 ± 1.5%), phosphate (87.76 ± 1.6%, 91.22 ± 1.5%), and SMBR achieved stable and excellent removal of COD (96.05 ± 0.2%, 97.39 ± 0.2%), TN (97.30 ± 0.3%, 97.44 ± 0.3%) andNH4+-N (99.07 ± 0.2%, 98.54 ± 0.2%) for swine wastewater and FW digestate, respectively. The effluent COD andNH4+-N concentrations were found to meet their discharge standards. The microbial community comparison showed similar diversity and richness, and genus Diaphorobacter and Thaurea were dominant in denitritation, and Nitrosomonas was dominant in nitritation treating both swine wastewater and FW digestate.

Profiles of antibiotic resistome and microbial community in groundwater of CKDu prevalence zones in Sri Lanka.

The chronic kidney disease of unknown etiology (CKDu) prevalent in certain regions of Sri Lanka poses a serious threat to human health. Previous epidemiological studies focused on the search of causative agents for CKDu etiology from the viewpoint of groundwater composition, but how CKDu prevalence affected the groundwater microbial composition, especially the antibiotic resistome, has never been illuminated. This study investigated the response of microbial community and antibiotic resistome to CKDu prevalence in the groundwater through the high throughput sequencing and qPCR (HT-qPCR), respectively. Results showed that CKDu prevalence significantly influenced the distribution of antibiotic resistome and microbial community composition. The mexF dominated in all the groundwater samples and could be considered as an intrinsic ARG, and the ß-lactamase cphA was specially enriched and closely associated with the antibiotics used for CKDu patients. The Acinetobacter was a potential human pathogen common in the groundwater of CKDu affected regions, while CKDu prevalence specially enriched the Aeromonas. Statistical analysis indicated that CKDu prevalence impacted antibiotic resistome through the microbial community as a whole, and MGEs contributed to the occurrence of mexF, while the enrichment of cphA could be attributed to the increase of Aeromonas.

Fouling of ion exchange membranes used in the electrodialysis reversal advanced water treatment: A review.

Electrodialysis self-reversal (EDR) technology has attracted in the treatment of water for domestic and industrial uses. The self-reversal consists of a frequent reversal of the direction of current between the EDR-cell electrodes to combat fouling of ion exchange membranes (IEMs). Irrespective of the EDR self-cleaning processes, the role of natural organic matter and their complexing ability with metal ions on IEMs fouling is partially understood. The objective of this review is to identify the research gaps present in the elucidation of IEM fouling routes. The common IEMs' foulants are identified, and several fouling mechanisms are briefly discussed. The effectiveness of self-cleaning mechanisms to reduce IEMs fouling is also be discussed. Dissolved organic carbon (DOC) possesses high chelation which forms metal complexes with di and trivalent cations found in water. The role of ternary complexes, e.g. M2+/3+-DOC and membrane surface, on membrane fouling via surface bridging, are also addressed. Finally, mitigation methods of IEMs membrane fouling are also discussed.

Assembling reduced graphene oxide with sulfur/nitrogen- "hooks" for electrochemical determination of Hg(II).

Herein the sulfur/nitrogen contained groups, serving as the "hooks" for electrochemical determination of Hg(II), were assembled on the reduced graphene oxide (hereafter SN-rGO) via a one-step facile hydrothermal method. The thiourea acts as a precursor for sulfur/nitrogen doping and partial reduction of graphene oxide. The SN-rGO was used to modify the glassy carbon electrode (GCE) for electrochemical detection of Hg(II) by square wave anodic stripping voltammetry (SWASV). The sulfur/nitrogen doping significantly improves the Hg(II) complexation by SN-rGO due to the creation of multifunctional groups on the graphene nanosheet. The SN-rGO modified electrode has excellent sensitivity (20.48 µA/µM) and limit of detection (LOD 8.93 nM) for Hg(II) detection. The newly developed Hg(II) sensing electrode possesses minimal interference for other ions typically found in natural waters. Therefore, it can be used for routine water quality monitoring. The fabrication of the SN-rGO electrode is rapid and low cost; hence, it offers a potential platform for environmental monitoring of toxic metal ions.

Mesoporous g-C3N4/ß-CD nanocomposites modified glassy carbon electrode for electrochemical determination of 2,4,6-trinitrotoluene.

A novel method using mesoporous g-C3N4 and ß-cyclodextrin nanocomposite (mpg-C3N4/ß-CD) for the electrochemical detection of 2,4,6-trinitrotoluene (TNT) is presented. The unique structure of the mesoporous g-C3N4/ß-CD nanocomposite facilitates both mpg-C3N4 electrocatalysis and ß-CD inclusion-complexation of the analytes. When compared to GCE or mpg-C3N4 modified GCE, the mpg-C3N4/ß-CD modified glassy carbon electrode exhibits superior performance in the detection of TNT. Hence, we used mpg-C3N4/ß-CD modified GCE for the development of TNT detection method using linear sweep voltammetry at -0.45 V reduction potential with 100 s accumulation time. The TNT calibration curve is linear within the 1-100 µM concentration range and the corresponding sensitivity and LOD values are 0.2 µA/µM and 68 ppb respectively. When p-nitrophenol and o-nitrophenol introduced into the matrix, the mpg-C3N4/ß-CD modified GCE sensor showed high selectivity and sensitivity to the nitroaromatic compounds. Optimized mpg-C3N4/ß-CD modified GCE sensor was used for the detection of TNT in a natural lake water sample with an 96.8% peak recovery. The results shown in work illustrate the potential of using g-C3N4/ß-CD modified GCE sensors in monitoring TNT and other nitroaromatic compounds in environmental analysis.

Ca2+ and SO42- interactions with dissolved organic matter: Implications of groundwater quality for CKDu incidence in Sri Lanka.

It has recently been proposed that recalcitrant dissolved organic carbon (DOC) in groundwater plays a potent etiological role in the peculiar distribution of chronic kidney disease of unknown etiology (CKDu). This study aims to elucidate the interactions of Ca2+ and SO42- with a model organic fraction of humic acid (SHA) to determine the possible relationship of CKDu incidence with the DOC in drinking water. XPS and FT-IR methods respectively determined the surface functional groups and chemical composition of protonated dissolved organic carbon (HDOC) in a CKDu high-risk zone (HR) of Sri Lanka and in SHA. Higher surface C composition (87.9%) and lower O (11.4%) were observed for HDOC from the HR region than for SHA (C: 73.8%, O: 24.7%). Aromatic C with less O-containing functional groups was observed in HDOC. The IR band at 1170 cm-1 confirms the formation of organic sulfonate (C-SO3-) on SHA. A band at 1213 cm-1 due to organic sulfonate in HDOC from the CKDu HR region was also identified. The IR band at 866 cm-1 evidenced the formation of CaCO3 on SHA above pH 7.4. XPS data confirmed the presence of sulfur oxidation states corresponding to SO32- and SO42- at 168.9 eV and 170.1 eV binding energies, respectively. The binding energies at 347 eV and 351 eV for Ca 2p3/2 and Ca 2p1/2 eV, respectively, confirmed the bidentate complexation of Ca2+ with COO- and sulfonate groups on SHA. The organic sulfonate formed is postulated as a uremic toxicant.

Construction of electrochemical sensing interface towards Cd(II) based on activated g-C3N4 nanosheets: considering the effects of exfoliation and protonation treatment.

There is an urgent need to construct highly selective low-cost sensors for fast detection of toxic metal ions such as cadmium. When compared with 3D bulk materials, 2D layered materials after activation treatments show superior performances for electrochemical metal ion detection. The bulk graphitic carbon nitride (hereafter b-g-C3N4) was prepared by thermal polymerization with urea as a precursor; it was then activated through ultrasonic liquid exfoliation and protonation which resulted in successful fabrication of activated ultrathin g-C3N4 nanosheets (hereafter a-g-C3N4). The a-g-C3N4-modified glassy carbon electrode demonstrates excellent electrochemical performances for Cd2+ detection with 22.668 µA/µM sensitivity and 3.9 nM LOD (S/N = 3) due to high specific surface area and active sites created on the 2D layered structure. The chemical interference of Pb2+, Cu2+, and Hg2+ on Cd2+ detection was minimal. We have also measured Cd2+ in natural water and rice samples using the newly developed a-g-C3N4-modified electrode with high spike recoveries. Our results demonstrate the potential applications of newly developed a-g-C3N4-modified electrode for rapid detection of toxic metal ions in different sample matrixes. Graphical Abstract The activated g-C3N4 nanosheets (a-g-C3N4) were synthesized and used to construct electrochemical sensors with high sensitivity and anti-interference performance.

Characterization of dissolved organic carbon in shallow groundwater of chronic kidney disease affected regions in Sri Lanka.

Number of Chronic Kidney Disease patients with no identifiable cause (Chronic Kidney Disease Unknown Aetiology, CKDu) are escalating in the North Central Province (NCP) of Sri Lanka. This study examined distribution of dissolved organic carbon (DOC) in shallow groundwater of three CKDu risk zones (high risk, HR; low risk, LR and no risk, NR) and a control zone (CR) from wet to dry seasons. The interactions of DOC with calcium and magnesium ions and metabolites of selected pesticides were also examined. The lowest CODMnDOC values of 0.60 ±â€¯0.19, 0.58 ±â€¯0.17 were reported in the DOC of the HR water in the wet and dry seasons, respectively, and this DOC fraction encompasses organic compounds with the lowest labile C with the highest aromaticity. Four distinct fluorescence DOC fractions in the HR water were identified with fulvic acid component associated as dominant non-labile C fraction. The essential building blocks of non-labile C were concentrated into molecular weight (MW) fraction II (900-1800 Da). The DOC source in all groundwater was identified as autochthonous (fluorescence index > 1.8). In the HR water, pentachlorophenol (PCP) was also detected in appreciable quantities. The factor loadings based on principal component analysis (PCA) showed a positive correlation between DOC and sulfate, calcium, total iron, PCP in the HR groundwater. Accordingly, it can be inferred that divalent cations (Ca2+, Mg2+) abundant in the HR groundwater interact with phenolate and carboxylate functional groups in DOC at alkaline pH.

Drinking water quality and chronic kidney disease of unknown etiology (CKDu): synergic effects of fluoride, cadmium and hardness of water.

High prevalence of chronic kidney disease of unknown etiology (CKDu) in some regions of the world is suspected mainly due to a toxin-mediated renal failure. We examined the incidence of CKDu and potable chemical water quality in a CKDu-affected region. This region has been identified as a high-risk zone for CKDu (location: latitude: 8.3500°-9.0000°, longitude: 80.3833°-81.3000°, North Central Province, NCP, Sri Lanka) by the World Health Organization (WHO). However, within this macro-region, small pockets of CKDu non-prevalence zones do exist; notably, the residents in those pockets consume spring water. Therefore, the drinking water quality of four areas, namely high-CKDu-prevalence areas (zone I), low-CKDu-prevalence area (zone II), the CKDu-free isolated pockets (zone III) and control areas (controls) were examined for F, Al, Cd, and As, and hardness and the statistical analysis were carried out to probe possible correlations among these parameters. The fluoride and hardness concentrations of water in zone III and control areas are much lower compared to zones I and II, and the water hardness is ~61 mg/L CaCO3. In zones I and II, the harness of drinking water is ~121-180 mg/L CaCO3; however, Al, Cd and As concentrations are almost comparable and below WHO recommendations. In most of the locations in zones I and II, the F concentration in drinking water is higher than the WHO recommendations. The peculiar distribution patterns of CKDu point to a synergic effect of trace elements in water for etiology of the disease.

Fluoride adsorption on γ - Fe2O3 nanoparticles.

BACKGROUND: Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide and hence its removal attracted much attention to have clean aquatic systems. In the present work, removal of fluoride ions from drinking water tested using synthesized γ-Fe2O3 nanoparticles. METHODS: Nanoparticles were synthesized in co-precipitation method. The prepared particles were first characterized by X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). Density functional theory (DFT) calculations on molecular cluster were used to model infrared (IR) vibrational frequencies and inter atomic distances. RESULTS: The average size of the particles was around 5 nm initially and showed a aggregation upon exposure to the atmosphere for several hours giving average particle size of around 5-20 nm. Batch adsorption studies were performed for the adsorption of fluoride and the results revealed that γ-Fe2O3 nanoparticles posses high efficiency towards adsorption. A rapid adsorption occurred during the initial 15 min by removing about 95 ± 3 % and reached equilibrium thereafter. Fluoride adsorption was found to be dependent on the aqueous phase pH and the uptake was observed to be greater at lower pH. Fourier transform infrared spectroscopy (FT-IR) was used for the identification of functional groups responsible for the adsorption and revealed that the direct interaction between fluoride and the γ-Fe2O3 particles. CONCLUSIONS: The mechanism for fluoride removal was explained using the dehydoxylation pathway of the hydroxyl groups by the incoming fluoride ion. FT-IR data and other results from the ionic strength dependence strongly indicated that formation of inner-spherically bonded complexes. Molecular clusters were found to be good agreement with experimental observations. These results show direct chemical interaction with fluoride ions.

Adsorption of dissolved aluminum on sapphire-c and kaolinite: implications for points of zero charge of clay minerals.

We have studied the impact of dissolved aluminum on interfacial properties of two aluminum bearing minerals, corundum and kaolinite. The effect of intentionally adding dissolved aluminum on electrokinetic potential of basal plane surfaces of sapphire was studied by streaming potential measurements as a function of pH and was complemented by a second harmonic generation (SHG) study at pH 6. The electrokinetic data show a similar trend as the SHG data, suggesting that the SHG electric field correlates to zeta-potential. A comparable study was carried out on kaolinite particles. In this case electrophoretic mobility was measured as a function of pH. In both systems the addition of dissolved aluminum caused significant changes in the charging behavior. The isoelectric point consistently shifted to higher pH values, the extent of the shift depending on the amount of aluminum present or added. The experimental results imply that published isoelectric points of clay minerals may have been affected by this phenomenon. The presence of dissolved aluminum in experimental studies may be caused by particular pre-treatment methods (such as washing in acids and subsequent adsorption of dissolved aluminum) or even simply by starting a series of measurements from extreme pH (causing dissolution), and subsequently varying the pH in the very same batch. This results in interactions of dissolved aluminum with the target surface. A possible interpretation of the experimental results could be that at low aluminum concentrations adatoms of aluminum (we will refer to adsorbed mineral constituents as adatoms) can form at the sapphire basal plane, which can be rather easily removed. Simultaneously, once the surface has been exposed to sufficiently high aluminum concentration, a visible change of the surface is seen by AFM which is attributed to a surface precipitate that cannot be removed under the conditions employed in the current study. In conclusion, whenever pre-treatment or the starting point of an experiment favor the dissolution of aluminum, dissolved Al may remain in the experimental system and interact with the target surfaces. The systems are then no longer pristine and points of zero charge or sorption data are those of aluminum-bearing systems.

Phyto-remediation potential of Ipomoea aquatica for Cr(VI) mitigation.

Phyto-remedial efficiency of Ipomoea aquatica was examined at different experimental conditions for a period of 3 months. This plant was selected due to its easy establishment, tolerance and growing easiness. In all trials, the I. aquatica was grown in coir dust to ensure an inert medium. Essential growth nutrients were supplied externally using Albert solution. Once plant growth conditions were fixed, the model system was spiked with Cr(VI) solution in the range of 7-90 ppm. Up to 28 ppm Cr(VI), I. aquatica exhibits uniform absorption characteristics showing over 75% removal of added Cr(VI). At this stage I. aquatica was not affected and it showed no toxicity symptoms. Therefore, it is suited as a potential phyto-remediant. Further I. aquatica is a vegetable particularly in Asian region; therefore caution has to be taken when selecting it for human consumption due to its high chromium accumulation capacity.