Poly(methacrylic acid)/SiO 2 /Al 2 O 3 based organic-inorganic hybrid adsorbent for adsorption of imazethapyr herbicide from aqueous medium

Insights into adsorption performance and mechanism of chitosan-bentonite biocomposites for removal of imazethapyr and imazamox

In the present study, chitosan-bentonite biocomposites were synthesised by ultrasonication, characterized using spectral techniques and assessed for their effectiveness in removing imazethapyr and imazamox from aqueous solution. The response surface methodology based box behnken design was utilized to generate optimum conditions viz. pH (1 to 9), adsorbent dose (0.01 to 1.0 g), contact time (0.5 to 48 h) and temperature (15 to 55 °C) for adsorption of herbicides on biocomposites. Based on model predictions, 60.4 to 91.5 % of imazethapyr and 31.7 to 46.4 % of imazamox was efficiently removed under optimal conditions. Adsorption data exhibited a strong fit to pseudo-second-order kinetic (R2 > 0.987) and Freundlich isotherm (R2 > 0.979). The adsorption capacity ranged from 3.88 to 112 μg1-ng-1mLn and order of adsorption was: low molecular weight chitosan-bentonite> medium molecular weight chitosan-bentonite> high molecular weight chitosan-bentonite> bentonite. Thermodynamic experiments suggested a spontaneous, exothermic process, reducing the system randomness during adsorption. Desorption experiments revealed successful desorption ranging from 91.5 to 97.0 % using 0.1 M NaOH. The adsorption mechanism was dominated by synergistic electrostatic interactions and hydrogen bonding. These results collectively indicated the potential environmental remediation application of chitosan-bentonite biocomposites to adsorb imazethapyr and imazamox from wastewaters.

Exploration of the biodegradation pathway and enhanced removal of imazethapyr from soil by immobilized Bacillus marcorestinctum YN1

Excessive or inappropriate applications of imazethapyr cause severe ecological deteriorations and health risks in human. A novel bacterial strain, i.e., Bacillus marcorestinctum YN1, was isolated to efficiently degrade imazethapyr, with the degradation pathways and intermediates predicted. Protein mass spectrometry analysis identified enzymes in strain YN1 potentially involved in imazethapyr biodegradation, including methylenetetrahydrofolate dehydrogenase, carbon-nitrogen family hydrolase, heme degrading monooxygenase, and cytochrome P450. The strain YN1 was further immobilized with biochar (BC600) prepared from mushroom waste (i.e., spent mushroom substrate) by pyrolysis at 600 °C to evaluate its degrading characteristics of imazethapyr. Scanning electron microscope observation showed that strain YN1 was adsorbed in the rich pore structure of BC600 and the adsorption efficiency reached the maximum level of 88.02% in 6 h. Both energy dispersive X-ray and Fourier transform infrared spectroscopy analyses showed that BC600 contained many elements and functional groups. The results of liquid chromatography showed that biochar-immobilized strain YN1 (IBC-YN1) improved the degradation rate of imazethapyr from 79.2% to 87.4%. The degradation rate of imazethapyr by IBC-YN1 could still reach 81.0% in the third recycle, while the bacterial survival rate was 67.73% after 180 d storage at 4 °C. The treatment of IBC-YN1 significantly shortened the half-life of imazethapyr in non-sterilized soil from 35.51 to 11.36 d, and the vegetative growth of imazethapyr sensitive crop plant (i.e., Cucumis sativus L.) was significantly increased in soil remediated, showing that the inhibition rate of root length and fresh weight were decreased by 12.45% and 38.49% respectively. This study exhanced our understanding of microbial catabolism of imazethapyr, and provided a potential in situ remediation strategy for improving the soil environment polluted by imazethapyr.

Synthesis & fabrication of O-linked polymeric hybrids for recovery of textile dyes: Closed loop economy

Dyes are an important resource employed for the production systems in textile, paper, paint and leather industry. An estimate of 200,000 tons of dyes are discharged as textile effluent each year worldwide. It becomes imperative to recover these dyes by treating the effluents using economically viable routes. The present research was undertaken with the objective to attain zero emission and zero waste through development of novel polymeric hybrids as adsorbents. For this purpose, metal moieties (Al3+, Si4+, Ti4+ and Zr4+) were hybridized with polyacrylic acid, and cellulose acetate for the uptake of selected dyes under optimized parameters. The structural elucidation of four synthesized hybrids (MP-Al, MP-Si, MP-Ti and MP-Zr) by FTIR, EDX and TGA confirmed O-linked grafting of metal moieties with polymers and thermally stable porous materials. SEM micrographic images displayed void spaces providing channels for effective adsorption. The batch experiments demonstrated removal of malachite green (77-96%) and congo red (70-82%) upon contact of initial 45 min on polymeric hybrids On the other hand, pristine polyacrylic acid and cellulose acetate showed remarkably low removal of dyes. The adsorption mechanism is proposed as physical in nature following type II isotherm. Further, Langmuir and Ho's pseudo second order fitness was evaluated. In order to determine the economic viability of the present research, the real textile dyes were recovered in three consecutive cycles of adsorption and chemical treatment of hybrids. The results propose a system with positive impact on economy by maximum utilization of hybrids as adsorbents and recovery of textile dyes for reuse in textile processing.

Insights into the microbiological and virulence characteristics of bacteria in orthopaedic implant infections: A study from Pakistan

The exponential increase in the prevalence of multidrug resistant bacteria has resulted in limiting surgical treatment options globally, potentially causing biofilm-related complications, implant failure, and severe consequences. This study aims to isolate and characterize bacteria from post-surgical orthopaedic implant infections and screening for multiple antibiotic resistance. A cross-sectional study was conducted, involving isolation of forty-four dominant pathogenic bacterial isolates from 16 infected implant samples from across Islamabad and Rawalpindi. Out of forty-four, 38% cocci and 61% bacilli were obtained. Approximately 90% of isolates showed multiple antibiotic resistance (MAR) index of more than 0.2. Eleven strains were identified via 16S rRNA gene sequencing as Pseudomonas aeruginosa, Bacillus spp., Planococcus chinensis, Staphylococcus, Escherichia coli and Enterobacter cloacae. The bacterial strain E. coli MB641 showed sensitivity to Polymyxin only, and was resistant to all other antibiotics used. Maximum biofilm forming ability 0.532 ± 0.06, 0.55 ± 0.01 and 0.557 ± 0.07 was observed in Pseudomonas aeruginosa MB663, Pseudomonas aeruginosa MB664 and Bacillus spp. MB647 respectively after 24 hours of incubation. EPS production of bacterial strains was assessed, the polysaccharides and protein content of EPS were found to be in the range of 11-32 μg/ml and 2-10 μg/ml, respectively. Fourier transform infrared spectroscopic analysis of EPS showed the presence of carbohydrates, proteins, alkyl halides, and nucleic acids. X-ray diffraction analysis revealed crystalline structure of EPS extracted from biofilm forming bacteria. These findings suggest a high prevalence of antibiotic-resistant bacteria in orthopaedic implant-associated surgeries, highlighting the urgent need for ongoing monitoring and microorganism testing in infected implants.

Development of Micro-Column Preconcentration Method Using a Restricted-Access Poly(protoporphyrin-co-vinyl pyridine) Adsorbent for Copper Determination in Water and Milk Samples by FIA-FAAS

For years, researchers have focused on the determination of metal ions at trace levels in environmental and food samples using analytical methods that employ techniques with low cost acquisition and maintenance and without microwave-assisted acid digestion procedures or aggressive reagents. Therefore, the present study deals with the synthesis and application of a novel, restricted-access poly(protoporphyrin-co-vinyl pyridine) adsorbent to preconcentrate copper in water samples and bovine milk that have only been subjected to pH adjusting (pH 6.0) and filtration using posterior on-line determination by FAAS. Regarding macromolecules, the restricted-access property of the adsorbent was achieved using the hydrophilic compound 2-hydroxyethyl methacrylate (HEMA). This method is based on the preconcentration of Cu2+ ions using a flow-injection system which is buffered with 0.05 mol L−1 of Britton–Robinson (BR) at a pH of 6.0 and has a flow rate of 14.0 mL min−1 through a mini-column packed with 50.0 mg of adsorbent. The elution was carried out using 0.40 mol L−1 of HCl toward the FAAS detector. The developed method provided a preconcentration factor of 44.7-fold, low limits of detection (LOD) (0.90 µg L−1) and quantification (LOQ) (2.90 µg L−1), tolerance to interfering ions (95.0 and 103.0%), and intra-day and inter-day precision assessed as the RSD (percentage of relative standard deviation), which ranged from 3.08 to 4.80%. The restricted-access poly(protoporphyrin-co-vinyl pyridine) adsorbent demonstrated outstanding features to exclude macromolecules, bovine serum albumin (BSA), and humic acid (HA) from an aqueous medium. Lake water and bovine milk samples were analyzed by the proposed preconcentration method with minimal sample pretreatment (which was based mainly on pH adjusting and filtration using an analytical curve with external calibration), yielding recovery values from addition and recovery tests ranging from 91.7 to 101.9%. The developed method shows great advantages over previously published methods, avoiding the time-consuming use of concentrated acids in a microwave-assisted acid digestion procedure.

Dissipation and phytotoxicity of imazethapyr and imazamox in soils amended with β-cyclodextrin-chitosan biocomposite

Use of imazethapyr and imazamox has been an environmental concern due to their high persistence, water solubility, residue build up and potential to injure the succeeding crops. Hence, it is necessary to develop effective decontamination technology. In present study, effect of β-cyclodextrin-chitosan biocomposite (LCD) amendment in soil on dissipation of imazethapyr and imazamox and their phytotoxicity on succeeding crop was evaluated. The influence of different experimental variables viz. extractant solution and its concentration, liquid to soil ratio, amount of soil and soil type on dissipation of imazethapyr and imazamox was assessed through chemical assays. Irrespective of herbicide formulation and application rate, amendment of soils with LCD increased the dissipation rate of herbicide and the residues were below the detection limit (<0.005 μg g^-1) within 5 to 15 days in aridisol, entisol, inceptisol A, inceptisol B, inceptisol C and 7 to 21 days in alfisol and vertisol. Amendment of soils with LCD significantly reduced the growth inhibition of Brassica juncea (L.) Czern and improved the soil biological activity as evident from increase in dehydrogenase activity and soil bacterial count. Amendment of soils with LCD could be a promising, economically feasible and environmentally benign soil decontamination strategy for imazethapyr and imazamox contaminated soils.

Development of selective preconcentration/clean-up method for imidazolinone herbicides determination in natural water and rice samples by HPLC-PAD using an imazethapyr imprinted poly(vinylimidazole-TRIM)

The development of a novel molecularly imprinted solid-phase extraction (MISPE) method for simultaneous preconcentration of imazapyr (IMP), imazapic (IMZ) and imazethapyr (IMT) with determination by HPLC-PAD (High performance liquid chromatography - photodiode-array detector) is proposed. The polymer synthesis was performed using imazethapyr as template molecule and 1-vinylimidazole as functional monomer. The method is based on preconcentration of 100.0 mL of sample through 200.0 mg of molecularly imprinted poly(vinylimidazole-TRIM) (MIP-1VN) at pH 4.0, followed by elution with 2.0 mL of MeOH:CH₂Cl₂:HAc (34:62:4, v/v). The range of analytical curve (0.29-200.0, 0.21-200.0 and 0.15-200.0 µg L^-1), limits of detection (0.09, 0.06 and 0.04 µg L^-1) and preconcentration factors (92, 96 and 98) determined for the herbicides, IMP, IMZ and IMT, respectively, were greatly superior when compared with those ones obtained with commercial adsorbents. The analytical method was successfully applied to spiked surface water and rice samples with good results of recovery values (86-107%).

Thermal Behavior and Structural Study of SiO₂/Poly(ε-caprolactone) Hybrids Synthesized via Sol-Gel Method

SiO₂-based organic-inorganic hybrids (OIHs) are versatile materials whose properties may change significantly because of their thermal treatment. In fact, after their preparation at low temperature by the sol-gel method, they still have reactive silanol groups due to incomplete condensation reactions that can be removed by accelerating these processes upon heating them in controlled experimental conditions. In this study, the thermal behavior of pure SiO₂ and four SiO₂-based OIHs containing increasing amount (6, 12, 24 and 50 wt %) of poly(ε-caprolactone) (PCL) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanisms of thermally activated processes occurring upon heating. In particular, all samples already release ethanol at low temperature. Moreover, thermal degradation of PCL takes place in the richest-PCL sample, leading to 5-hexenoic acid, H₂O, CO₂, CO and ε-caprolactone. After the samples' treatment at 450, 600 and 1000 °C, the X-ray diffraction (XRD) spectra revealed that they were still amorphous, while the presence of cristobalite is found in the richest-PCL material.