Qe Values Research Articles

Chemically modified activated carbon decorated with MnO2 nanocomposites for improving lithium adsorption and recovery from aqueous media

Lithium (Li+) is considered as promising element in a variety of fields, including medicine, manufacturing, dyes, and the glass industry. Thus, the need for lithium has continued to escalate. Chemically modified activated carbon (CAC) supported with manganese dioxide (MnO2) nanoparticles was prepared using different manganese salt concentrations (0.1, 0.15, 0.12 and 0.2 M), a facile impregnation approach for enhancing the capacity of activated carbon for Li+ adsorption from aqueous media. The structural, morphological, physico-chemical and elemental properties were characterized by FE-SEM, EDAX, FE-TEM, FTIR, XRD, BET and ICP-OES. A batch experiment was performed to optimize the parameters (pH, adsorbent dose, and contact time) for Li+ adsorption. A kinetic study indicated that lithium sorption process followed a pseudo-second order reaction. Comparative analysis revealed that adsorption capacity of CAC increased with an increase in manganese loading, CAC-Mn0.1, CAC-Mn0.12, CAC-Mn0.15, and CAC-Mn0.2 with qe values of 50.1 mg/g, 65.04 mg/g, 69.93 mg/g and 88.5 mg/g respectively. A desorption study was performed to illustrate the benefits of sorbents by using HCl as an eluting agent. The competitive Li+ adsorption and reusability property during four adsorption/desorption cycle showed high selective Li+ adsorption with regeneration tendency, which enable the synthesized nanocomposites as potential candidature adsorbents for lithium recovery from aqueous solution.

Chromium ion removal from raw water by magnetic iron composites and Shewanella oneidensis MR-1

In this study, nanoiron active carbon composites (NZVI/GAC) were used to remove chromium ions from raw water. The composites were synthesized from a novel formula of biological activated carbon and characterized by various techniques. The adsorption test data were fit by a pseudo-second-order kinetic model and Langmuir model. The qe and R2 values were 187 mg Cr/g and 0.9960, respectively, with 0.2 g/L NZVI/GAC at an initial concentration of 118 mg/L Cr according to the Langmuir isotherm model. Moreover, a Cr6+ detoxification reactor was constructed with the magnetic iron composite. The results indicated that the synthesized magnetic iron composite was a significant adsorbent for Cr6+ removal from aqueous solutions. The detoxification reactor was able to remove Cr6+ from raw water at an initial concentration of 26.5 mg/L within a short time period (3–5 min), with a removal efficiency of up to 99.90% and a treatment capacity of 45.0 mg Cr6+/g of adsorbent; the Cr6+ concentrations in the outflow met the GB5749–2006 requirements for drinking water. A synergistic effect between NZVI/GAC and a suspension of the bacterium Shewanella oneidensis MR-1 was found, showing that this bacterium can be used as a regeneration agent for iron-depleted activated carbon materials.

A comparison of the characteristics and atrazine adsorption capacity of co-pyrolysed and mixed biochars generated from corn straw and sawdust

The biochar used in this study was prepared from corn straw and sawdust mixed in a ratio of 1:1 (m/m) at temperatures of 300 °C and 800 °C, which adopted the methods of co-pyrolysis (BC300A and BC800A) and mixing of single biochar (BC300B and BC800B). The obtained biochar was characterized by SEM, BET and FTIR analysis. Adsorption properties, including the atrazine adsorption kinetics and isotherms of the four kinds of biochar to atrazine, were investigated. The results showed that a pseudo-second order kinetic model was suitable for describing the adsorption of atrazine by BC800B because its R2 value is greater than the pseudo-first order model. The adsorption capacity (qe) of BC800B, blended from the two single biochars produced at 800 °C, is 37.2 mg g−1, which is better than that of the other three species. This value is 4–6 times the qe values of BC300A, BC300B and BC800A, which are 6.74 mg g−1, 7.77 mg g−1 and 5.26 mg g−1, respectively. At higher pyrolysis temperature, the pore structure of biochar is more developed, the specific surface area is larger, and the species and number of surface functional groups are also significantly different. At the same time, the results also showed that the order of mixing and pyrolysis affected the characteristics and adsorption capacity of biochar. This study reveals the atrazine adsorption mechanism of four kinds of biochar and provides information about the potential of these types of materials for the removal of atrazine in the aquatic environment.

The influence of carbon counter electrode composition on the performance of monolithic dye-sensitized solar cells

In this research, the influence of carbon composition on the physical and electrical characteristics of the counter electrode and the performance of monolithic dye-sensitized solar cell (DSSC) was investigated. Screen printing method was used due to its excellence such as simple fabrication process at mass production. Physical and electrical characterization of the counter electrode layer were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, gas sorption using Brunauer-Emmett-Teller (BET) method, and four-point probe measurement. Meanwhile, the DSSC performance was characterized using current-voltage (I-V) and incident photon-to-current efficiency (IPCE) measurement system. It is found that the carbon composition affects the physical and electrical characteristics of the counter electrode, such as the porosity, crystallinity, BET surface area, and micro-sized agglomeration. However, relatively similar conductivity values are obtained regardless of the carbon composition. The results show that the composition of graphite and active carbon with a ratio of 1:4 as a counter electrode material produced a porous layer with approximately 3.32 μm of agglomerates and conductivity with a sheet resistance value of 11.60 Ω/sq that overall can improve the performance of the monolithic DSSC. The highest efficiency obtained is 1.52% and the highest QE value is 32% at the absorption area of TiO2, with Voc, Isc and Pmax value of 0.63 V, 1.19 mA and 0.91 mW, respectively.

Removal of aniline from aqueous solution by activated kaolinite: Kinetic, equilibrium and thermodynamic studies

In this study, the adsorption kinetics, equilibrium and thermodynamics of aniline on native (NK) and acid activated (AK) kaolinites were examined. It was shown that modification of kaolinite with acid not only increases the adsorption capacity of the adsorbent from 109.89 to 256.41 mgg−1for aniline but also its initial sorption rate for aniline, suggesting the activated kaolinite with higher adsorption capacity have great potential application in removal of aniline from water and wastewater. Adsorption efficiency for AK reached at about 91% while it was at about 75% for NK. The kinetics of adsorption of aniline was discussed using three kinetic models, the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted very well the pseudo-second-order kinetic model due to the higher correlation coefficient and lower sum of squared errors (SSE,%) values, and a good agreement between the experimental and the calculated qe values. Experimental results were also analysed by the Langmuir, Freundlich and Dubinin–Redushkevich (D–R) isotherm models. RL separation factor for Langmuir and the n value for Freundlich isotherm show that aniline are favourably adsorbed by NK and AK. The negative value of ΔG and positive value of ΔS showed that the adsorption of aniline onto NK and AK was feasible and spontaneous. The positive value of ΔH confirmed the endothermic nature of adsorption.

Kinetics and Adsorption Isotherm Studies of Methylene Blue Photodegradation Under UV Irradiation Using reduced Graphene Oxide- TiO2 Nanocomposite in Different Wastewaters Effluents.

In this study TiO2@rGO nanoparticles was synthesized as an effective photocatalyst. Reduced graphene oxide (rGO) was mixed with TiO2 with different doping ratio (1%, 3% and 5% wt) and utilized to remove MB dye as organic pollutants from different wastewater effluents and also from aqueous solution. The impacts of different factors, e.g. pH of solution, contact time, photocatalyst dose and initial MB dye concentration on the removal efficiency were studied. The results showed that the highest MB degradation occurred at pH 9, contact time = 120 min, dose of photocatalyst of 0.75 g/L at 30 mg/l dye concentration. Also, the prepared nanocomposites success in reducing COD values of wastewater in the range of 30 – 89.1 %. Moreover, the data of kinetics studies indicated that the adsorption process well obeys the pseudo-second order reaction model with qe values ranged between 14.28 – 19.37 mg/L. Langmuir isotherm model well describes the behavior of adsorption behavior than Freundlich Model.

Construction of Nonmetallic p‐n Heterojunction With Face‐to‐Face Structure for Drastically Enhanced Photocatalytic Performance

AbstractIt is still a great challenge to exploit high‐efficiency nonmetallic composite photocatalysts by structural design for improving H2 production performance. Here, the nonmetallic p‐n heterojunctions with face‐to‐face structure are prepared via hydrothermal in‐situ polymerization of PEDOT on the surface of g‐C3N4. The face‐to‐face modification of PEDOT on g‐C3N4 not only broadens the response in the visible light region but also increases the electron delocalization of conjugated system, which results in improving the visible light harvest ability and separation efficiency of charge carriers. The obtained PEDOT/g‐C3N4 heterojunctions display the improved H2 production activity, and the optimal H2 production rate reaches up to 3636.6 μmol g−1 h−1 with QE value of 5.6% at 420 nm, which is 5.46 times higher than that of pure g‐C3N4 (665.8 μmol g−1 h−1).

Selective removal of tungstate anions from aqueous solutions by surface anion‐imprinted ceramic membranes

AbstractBACKGROUNDIt is significantly important to develop new technologies and materials for removal of tungstate anions (W(VI)) from aqueous solutions. An ion imprinted membrane not only possesses all virtues of a separation membrane, but also has tailor‐made recognition sites. In this work, a novel surface anion‐imprinted ceramic membrane (IIP‐PEI/CM) was fabricated to remove W(VI) selectively from aqueous solutions.RESULTSFT‐IR, XPS, TGA, SEM, streaming potential, pore size distribution and water flux confirmed the successful fabrication of IIP‐PEI/CM. With increasing pH, binding capacities (Qe) of W(VI) onto IIP‐PEI/CM and non‐imprinted membrane (NIP‐PEI/CM) rapidly decreased. At pH = 2.0, Qe values of IIP‐PEI/CM and NIP‐PEI/CM were 139.4 and 47.9 mg 100 g−1, respectively. Binding equilibrium was achieved within 3 min, showing an ultra‐fast kinetic process. Compared with NIP‐PEI/CM, IIP‐PEI/CM had higher selectivity for W(VI) in the presence of Mo(VI) and Cr(VI) ions, and its selectivity coefficients for W(VI)/Mo(VI) and W(VI)/Cr(VI) were 15.47 and 19.74, respectively. During dynamic filtration, IIP‐PEI/CM was effective and selective for removal of W(VI), and it had a good reusability. Protonated amine groups within PEI participated the uptake of W(VI) by electrostatic interactions.CONCLUSIONIIP‐PEI/CM showed ultrafast and selective binding of W(VI) anions, and has potential application for W(VI) removal/recovery from aqueous solutions. © 2018 Society of Chemical Industry

Epoxide functionalized γ‐Al2O3/Fe3O4/SiO2 nanocomposite and comparative adsorption behavior of a model reactive azo dye

AbstractIn this investigation, magnetic γ‐Al2O3 nanocomposite polymer particles with epoxide functionality were prepared following a multistep process. The prepared nanocomposite polymer particle was named as γ‐Al2O3/Fe3O4/SiO2/poly(glycidyl methacrylate (PGMA). The surface property was evaluated by carrying out the adsorption study of Remazol Navy RGB (RN), a model reactive azo dye, on both γ‐Al2O3/Fe3O4/SiO2 and γ‐Al2O3/Fe3O4/SiO2/PGMA nanocomposite particles, that is, before and after epoxide functionalization. A contact time, temperature, adsorbent dose, and dye concentration dependent change in adsorption behavior was observed on both nanocomposite particles. The adsorption amount reached equilibrium (qe) value within 5 minutes at the respective point of zero charge (PZC). The adsorption density of RN per unit specific surface area on epoxide functional γ‐Al2O3/Fe3O4/SiO2/PGMA nanocomposite polymer particles (1.30 mg/m2) was higher relative to that on γ‐Al2O3/Fe3O4/SiO2 nanocomposite particles (0.87 mg/m2). The optimum adsorbent dose for obtaining the maximum adsorption density was 0.01 g. Comparatively, Langmuir isotherm model was better to describe the adsorption process and the adsorption process was favorable at low temperature (283 K). Batch kinetic adsorption experiment suggested that a pseudo‐second‐order rate kinetic model is more appropriate. Nanocomposite polymer particles were used as adsorbent up to third cycle with almost 99% adsorption efficiency.

Removal of Cr(VI) from aqueous solution using functionalized poly(GMA-co-EGDMA)-graft-poly(allylamine)

To remove Cr(VI) from aqueous solution, a macroporous poly glycidyl methacrylate-co- ethylene glycol dimethacrylate (poly(GMA-co-EGDMA)) adsorbent was synthesized by radical suspension copolymerization. Allylamine was used to open the epoxy ring of the prepared copolymer, then the radical polymerization of the grafted allylamine was performed, and as the last step, methyl isothiocyanate (MITC) was reacted with the crosslinked graft copolymers to introduce the thiourea groups. The introduced amine and thiourea functional groups enabled the effective removal of Cr(VI). The polymer was analyzed by FT-IR spectroscopy, FE-SEM, and mercury porosimetry, and the chemical structure, surface morphology and pore characteristics of the polymer were confirmed. The pH of the Cr(VI) solution strongly affected the performance of the adsorbent, and the best removal efficiency was obtained at pH 2. In the kinetic studies, the qe value determined from the pseudo-second-order model was similar to the experimental qe value, and this model showed the best correlation. The isotherm data were better fit by the Langmuir adsorption isotherm model than the Freundlich isotherm model, and the maximum adsorption capacity was 166.24 mg/g.

Adsorption of U(VI) from eutrophic aquesous solutions in a U(VI)-P-CO3 system with hydrous titanium dioxide supported by polyacrylonitrile fiber

Hydrous titanium dioxide supported by commercially available polyacrylonitrile fiber (c-PANF/TiO2·xH2O) was synthesized via a simple blending method to first investigate its U(VI) adsorption behavior from eutrophic aqueous solution in a U(VI)-P-CO3 system. TG-DSC and XRD analysis demonstrated that the material had good structural stability during the adsorption process. The theoretical maximum U(VI) adsorption capacity (qe) of c-PANF/TiO2·xH2O calculated from the Langmuir isotherm was ~256 mg/g. However, high initial solution pH values, total dissolved carbonate concentration and ionic strength could inhibit U(VI) chemisorption. In particular, qe and sorption efficiency (S%) values were maintained at ~100 mg/g and > 80% for the [P] range of 0 to 150 μmol/L, and then they rapidly decreased once [P] exceeded 150 μmol/L due to the competitive adsorption between HPO42-/H2PO4- and uranium anionic complexes such as UO2(CO3)34−, UO2(CO3)22− and UO2PO4-. XPS analysis suggested that Ti3+ defects and OH groups on the composite surface could be the U(VI) adsorption sites. Moreover, a 0.1 mol/L H2SO4 solution was found to be the most effective desorption agent. The findings reported in this study are significant in regards to the extraction of uranium from eutrophic seawater and for the understanding of uranium adsorption behaviors in multi-carbonate systems.

Study of sorption and desorption of Cd (II) from aqueous solution using isolated green algae Chlorella vulgaris

In the present investigation, isolated green algae Chlorella vulgaris has been proven to be a very effective and promising adsorbing biomaterial for Cd (II) removal from aqueous solution in batch experiments. Adsorption features of algae were studied as function of time, pH, initial Cd (II) concentration and algal biomass dosages. Kinetics and adsorption equilibrium isotherms of algal biomass were obtained for batch experiments. Kinetic data were best fitted to the pseudo-second-order where adsorption capacity (qe) values agree to experimental values. Langmuir isotherm model which shows the existence of monolayer adsorption under the experimental conditions best fitted to the obtained equilibrium data. The maximum adsorption capacity calculated by Langmuir model was 97.43 mg/g. FTIR, SEM, metal mapping were performed for virgin algal biomass and biomass loaded with Cd (II) to analyze the mechanism of adsorption. The various parameters of thermodynamics viz, ΔH, ΔG and ΔS, show endothermic, feasible and spontaneous behaviour, respectively, in sorption process. Desorption experiments were carried out insight of various parameters which resulted 0.1 M EDTA had commanding recovery of Cadmium metal ions. Recyclability study of algal biomass indicates promising future as it remains unaffected after five cycles with very less adsorption capacity loss (5.8%).

Synthesis of phosphorylated raw sawdust for the removal of toxic metal ions from aqueous medium: Adsorption mechanism for clean approach

In this work, phosphorus oxychloride was grafted onto the surface of raw sawdust (RSD) particles to get effective adsorbent for capturing Cd(II), Cr(III), and Pb(II) metal ions from aqueous medium. Phosphorylated raw sawdust (RSD@P) was characterized by FTIR, TGA, SEM-EDX, TEM, BET, and XPS analyses. Various experimental conditions of adsorption viz. pH, contact time, temperature, and initial concentration were optimized. The adsorption behavior of RSD@P concerning adsorption kinetics, isotherms and thermodynamics was also studied. The values of qe for Cd(II), Cr(III), and Pb(II) metal ions onto RSD@P was found to be 244.3, 325, and 217 mg/g, respectively at 298 K according to monolayer Langmuir adsorption. The adsorption kinetics data revealed that Cd(II), Cr(III), and Pb(II) metal ions were well fitted to pseudo-second-order kinetic model. The thermodynamic results demonstrated that adsorption was spontaneous and exothermic. The mechanisms of interactions was also discussed for the adsorption of Cd(II), Cr(III), and Pb(II) metal ions over RSD@P. The obtained results showed that RSD@P was an auspicious adsorbent which showed outstanding reusability for the removal of metal ions from aqueous medium.

Influence of shallow versus deep etching on dark current and quantum efficiency in InAs/GaSb superlattice photodetectors and focal plane arrays for long wavelength infrared detection

In this paper, a comparison of quantum efficiency and dark current densities of shallow etched and deep etched InAs/GaSb type-II superlattice photodiodes is presented. The detectors were tailored for space applications with measured cut-off wavelengths around 11.2 µm. Bias and temperature dependencies of the QE have been studied showing very low turn on bias (>−25 mV) and very small variation of the peak QE value with temperature. At 70 K, peak quantum efficiencies of shallow and deep etched devices were deduced to 34% and 30%, respectively (without antireflection coating). The difference was attributed to a larger collection area of shallow etched devices, with a collection range of approximately 22 µm outside of the defined pixel area. Diffusion limited dark currents were observed down to 60 K for both shallow and deep etched devices under low reverse bias (∼−200 mV) with dark current densities on the order of 1.7 × 10−5 A/cm2 at 60 K. A gradually increasing influence of generation-recombination (G-R) and trap-assisted tunneling (TAT) was observed at lower temperatures for high reverse bias. The lowest dark current densities were observed for deep etched photodiodes, on the order of 3 × 10−7 A/cm2 at 40 K (Vbias = −100 mV). Detector arrays were fabricated with deep etched 30 µm pitch pixels. Comparably low dark current densities were observed for the detector array pixels under low reverse bias as for the single pixel photodiodes, however a significant increase of the TAT dark current was observed under high reverse bias.

Taguchi design-based enhancement of heavy metals bioremoval by agroindustrial waste biomass from artichoke

The Taguchi method of designing experiments is based on a system of tabulated designs (arrays) that enables the maximum number of variables to be estimated in a neutral (orthogonal) balanced manner with a minimum number of experimental sets. Heavy metals remediation of aqueous streams is of special concern due to its highly toxic and persistent nature. Taguchi approach was used for enhanced bioadsorptive removal of Pb(II), Cu(II) and Cd(II) from aqueous solutions using agroindustrial waste biomass from globe artichoke as inexpensive sorbent. Sorbent biomass was characterized as to its chemical composition by infrared spectroscopy (FTIR), revealing the presence of hydroxyl, carboxyl, sulphonic and amine functional groups. Ranks of four factors (pH, temperature, sorbent dosage and initial metal concentration) at three levels each, in a L9 array were conducted, in batch sorption tests, for the individual metal ions of concern. The sorption capacity (qe) values were transformed into an accurate signal-to-noise (S/N) ratio for a “higher is better” response. The best conditions for individual heavy metal sorption were determined reaching up to 86.2 mg·g−1 for Pb, 35.8 mg·g−1 for Cd and 24.4 mg·g−1 for Cu. This paper also discusses the equilibria and kinetic aspects of the sorption process. Sorption isotherms were successfully described by the Sips model. In addition, the experimental data showed that the uptake kinetic profiles of the three metal ions closely fitted the pseudo-second order model. Conclusively, the agroindustrial waste biomass from globe artichoke represents a potentially viable sorbent for the bioremoval of Pb(II), Cu(II) and Cd(II) ions from aqueous systems.

Structure relationship of non–covalent interactions between phenolic acids and arabinan–rich pectic polysaccharides from rapeseed meal

Covalent and non–covalent interactions between polyphenols and polysaccharides produced vital consequences on the sensory and nutritive qualities of the many foods. In the present study, the structure dependence of the non–covalent interactions between phenolic acids (PAs) and an arabinan–rich pectic polysaccharide from rapeseed meal (ARPP) was explored. Native RAPP and its hydrolysates as well as twenty–seven structurally diversified PAs were applied. The interaction was determined as the micrograms of PAs adsorbed by per milligram of polysaccharides (Qe, μg/mg). On one hand, the molecular weight (Mw) of ARPP displayed a significant effect on the Qe of ferulic acid and a highest value (412.28 μg/mg) was obtained for the ARPP hydrolysate having a Mw of 76 kDa. On the other hand, the substituent profile of PAs greatly affected their Qe values onto ARPP, although the results are monomer and substituent specific. Specifically, in terms of Qe, hydroxylation favored the interaction by 35.78% to 271.22%, while methylation and esterification weakened the absorption by 44.78% to 230.71% and 16.48% to 78.68%, respectively. The case of esterification is more complicated that the attachment of OCH3 at 3–position (−26.14% to −77.04%) is adverse but that at 5–position is highly favorable (156.96% to 190.70%) for the interactions.

ROC75 is an Attenuator for the Circadian Clock that Controls LHCSR3 Expression.

Strong light intensity leads to harmful overexcitation of the photosystems in green algae. In Chlamydomonas reinhardtii, LHCSR3 is required for the rapid protective response known as energy-dependent quenching (qE). Because the majority of photoacclimation analysis has been conducted under controlled laboratory conditions, physiological responses to natural environmental changes such as light/dark cycles have not been examined in detail. Regarding fitness in higher plants and microalgae, light-dark cycles represent a major Zeitgeber for synchronizing the circadian clock to multiple physiological responses, yet there is little consensus with respect to the clock response to high-intensity light in photosynthetic organisms. In a previous study, 105 circadian rhythm insertional mutants were isolated as rhythm of chloroplast (roc) mutants. Here, we report our characterization of the roc75 mutant, which exhibited a significantly higher qE value and LHCSR3 protein accumulation when grown under red light. We performed transcript analysis of ROC75 in the pcry (plant-cryptochrome) and phot mutants and found that only the former accumulated lower levels of ROC75 mRNA, suggesting that the blue light photoreceptor pCRY positively regulates ROC75. However, the degradation of pCRY by high-light exposure contributes to prevent over-accumulation of ROC75, which in turn facilitates the PHOT mediated main activation pathway for LHCSR3. Furthermore, LHCSR3 mRNA exhibited a circadian rhythm, though its basal expression level in the roc75 mutant was higher than that in WT. We therefore conclude that ROC75 acts as an attenuator of the circadian clock to control LHCSR3 expression with blue and red light as stimuli for attenuation.

Adsorptive removal of dibenzothiophene from petroleum distillates using pomegranate leaf (Punica granatum) powder as a greener adsorbent

In this study, adsorption performance of pomegranate leaf powder (PLP) for the removal of dibenzothiophene (DBT) from petroleum distillates is presented. Morphology and elemental composition, surface chemistry, and textural property of the PLP were checked using scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and N2 physi-sorption at 77 K, respectively. Model oil contained 0.1 g DBT in 100 mL hexane was used for the performance evaluation and conducted in batch mode. The results show DBT removal of 70.55%, with the adsorbent retaining about 97.81% of its capacity after fourth cycle of usage. Results from SEM-EDX and FTIR indicate that DBT was adsorbed on the surface of PLP. Adsorption isotherm data fitted onto Freundlich and Langmuir isotherms models show very good coefficient of determination (R2) values of 0.9952 (for Langmuir) and 0.9979 (for Freundlich), indicating suitability of the models to describe the process. The adsorption kinetics of DBT onto PLP follows pseudo-second-order kinetics and the experimental qe (53.66 mg/g) values obtained is very close to the model-estimated value qe (55.55 mg/g). The negative value of ΔGo and the positive values of ΔHo obtained in the thermodynamic studies indicate that adsorption of DBT onto the PLP is an endothermic and spontaneous process at the temperatures studied.

Novel method for in situ investigation into graphene quantum dots effects on the adsorption of nitrated polycyclic aromatic hydrocarbons by crop leaf surfaces

Nitrated polycyclic aromatic hydrocarbons (NPAHs) are PAH derivatives with more toxic effects to ecosystem, and the partitioning of NPAHs in crop system constitutes the potential exposure to human health through the dietary pathway. In the present study, a novel method for in situ detection of 9-nitroanthracene (9-NAnt) and 3-nitrofluoranthene (3-NFla) adsorbed onto the leaf surfaces of living soybean and maize seedlings was established based on the fiber-optic fluorimetry combined with graphene quantum dots (GQDs) as a fluorescent probe. The detection limits for the in situ quantification of the two adsorbed NPAHs ranged from 0.8 to 1.6 ng/spot (spot represents determination unit, 0.28 cm2 per spot). Using the novel method, the effects of GQDs on the adsorption of individual 9-NAnt and 3-NFla by the living soybean and maize leaf surfaces were in situ investigated. The presence of GQDs altered the adsorption mechanism from the sole film diffusion to the combination of film diffusion and intra-particle diffusion, and shortened the time required to achieving adsorption equilibrium by 15.8–21.7%. Significant inter-species and inter-chemical variability existed in terms of the equilibrated adsorption capacity (qe) with the sequence of soybean > maize and 3-NFla > 9-NAnt. The occurrence of GQDs enlarged the qe values of 9-NAnt and 3-NFla by 22.8% versus 28.7% for soybean, and 16.2% versus 20.3% for maize, respectively, which was largely attributed to GQDs-induced expansion to the surface area for adsorbing NPHAs and the stronger electrostatic interaction between the -NO2 of NPAH molecules and the functional groups (e.g., -COOH, -OH) of GQDs outer surfaces. And, the varied enhancement degrees in the order of 3-NFla > 9-NAnt might be explained by the steric effects that resulted in the easier accessibility of -NO2 of 3-NFla to the outer surface of GQDs. Summarily, the GQDs increased the retention of NPAHs on crop leaf surfaces, potentially threatening the crop security.

Synthesis, characterization and adsorption studies of amino functionalized silica nano hollow sphere as an efficient adsorbent for removal of imidacloprid pesticide

In the present research, silica nano hollow sphere (SNHS) and amino functionalized silica nano hollow sphere (SNHS-NH2) adsorbents have been used to remove imidacloprid as a high consumption pesticides from aqueous solutions. SNHS and SNHS-NH2 have been synthesized based on our previously reported methods. FT-IR and SEM techniques have been employed to analyze physicochemical characteristics of produced adsorbents. The adsorption of imidacloprid has been evaluated in terms of kinetic and equilibrium on used different synthesized adsorbents. The adsorption tests were performed in various conditions, in addition to assess the effects of pH, temperature and adsorbent dosage. Equilibrium empirical data have been fitted by Langmuir, Sips, Freundlich, Toth, Khan, Tempkin and Redlich-Peterson isotherms. Correlation coefficients demonstrated that equilibrium data were better matched with the Redlich-Peterson (R-P) isotherm. On the other hand, experiments showed that the amount of adsorbate per unit mass of adsorbent is decreased by increasing of the pH, and the maximum value of qe is obtained in acidic pH. In addition, the amount of adsorbate per unit mass of adsorbent is reduced by rising temperature and the equilibrium adsorption is dropped by increasing the amount of silica adsorbent. Kinetic data have been fitted with Elovich, pseudo-first-order and pseudo-second-order models; according to the obtained correlation coefficients. It can be stated that the pseudo-first-order model is more suited to the kinetic data related to pesticide adsorption on silica adsorbent. Kinetics of imidacloprid adsorption has been investigated at the concentrations of 7.2 mg/L and 10 mg/L. The results demonstrated that the equilibrium rate slope become much steeper in the initial times by increasing concentrations of imidacloprid.