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    Chemical activation of atom-precise Pd3 nanoclusters on γ-Al2O3 supports for transfer hydrogenation reactions
    (Royal Society of Chemistry, 2024-09-30) Singh, Siddhant; Wi, Dami; Salem, Kholoud E.; Higgins, Drew
    Deposition of atom-precise nanoclusters onto solid supports is a promising route to synthesize model heterogeneous catalysts. However, to enhance nanocluster-support interactions, activation of the nanoclusters by removal of surface ligands is necessary. Thermal treatment to remove surface ligands from supported metal nanoclusters can yield highly active heterogeneous catalysts, however, the high temperatures employed can lead to poor control over the final size and speciation of the nanoclusters. As an alternative to high-temperature thermal treatments, chemical activation of [Pd3(μ-Cl)(μ-PPh2)2(PPh3)3]+ (Pd3) nanoclusters on γ-Al2O3 supports under mild reaction conditions has been demonstrated in this work. Hydride-based reducing agents such as NaBH4, LiBH4, and LiAlH4 have been examined for the activation of the Pd3 nanoclusters. The structural evolution and speciation of the nanoclusters after activation have been monitored using a combination of XAS, XPS, STEM-EDX mapping, and solid-state NMR techniques. The results indicate that treatment with borohydride reducing agents successfully removed surface phosphine and chloride ligands, and the extent of size growth of the nanoclusters during activation is directly correlated with the amount of borohydride used. Borate side products remain on the γ-Al2O3 surface after activation; moreover, exposure to high amounts of NaBH4 resulted in the incorporation of B atoms inside the lattice of the activated Pd nanoclusters. LiAlH4 treatment, on the other hand, led to no significant size growth of the nanoclusters and resulted in a mixture of Pd single-atom sites and activated nanoclusters on the γ-Al2O3 surface. Finally, the catalytic potential of the activated nanoclusters has been tested in the transfer hydrogenation of trans-cinnamaldehyde, using sodium formate/formic acid as the hydrogen donor. The catalytic results showed that smaller Pd nanoclusters are much more selective for hydrogenating trans-cinnamaldehyde to hydrocinnamaldehyde, but overall have lower activity compared to larger Pd nanoparticles. Overall, this study showcases chemical activation routes as an alternative to traditional thermal activation routes for activating supported nanoclusters by offering improved speciation and size control.
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    A Highly Sensitive Chitosan-Based SERS Sensor for the Trace Detection of a Model Cationic Dye
    (MDPI, 2024-08-28) Vafakish, Bahareh; Wilson, Lee
    The rapid detection of contaminants in water resources is vital for safeguarding the environment, where the use of eco-friendly materials for water monitoring technologies has become increasingly prioritized. In this context, the role of biocomposites in the development of a SERS sensor is reported in this study. Grafted chitosan was employed as a matrix support for Ag nanoparticles (NPs) for the surface-enhanced Raman spectroscopy (SERS). Chitosan (CS) was decorated with thiol and carboxylic acid groups by incorporating S-acetyl mercaptosuccinic anhydride (SAMSA) to yield CS-SAMSA. Then, Ag NPs were immobilized onto the CS-SAMSA (Ag@CS-SAMSA) and characterized by spectral methods (IR, Raman, NIR, solid state 13C NMR with CP-MAS, XPS, and TEM). Ag@CS-SAMSA was evaluated as a substrate for SERS, where methylene blue (MB) was used as a model dye adsorbate. The Ag@CS-SAMSA sensor demonstrated a high sensitivity (with an enhancement factor ca. 108) and reusability over three cycles, with acceptable reproducibility and storage stability. The Raman imaging revealed a large SERS effect, whereas the MB detection varied from 1–100 μM. The limits of detection (LOD) and quantitation (LOQ) of the biocomposite sensor were characterized, revealing properties that rival current state-of-the-art systems. The dye adsorption profiles were studied via SERS by fitting the isotherm results with the Hill model to yield the ΔG°ads for the adsorption process. This research demonstrates a sustainable dual-function biocomposite with tailored adsorption and sensing properties suitable for potential utility in advanced water treatment technology and environmental monitoring applications.
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    Cu(II) Ion Adsorption by Aniline Grafted Chitosan and Its Responsive Fluorescence Properties
    (MDPI, 2020-02-26) Vafakish, Bahareh; Wilson, Lee
    The detection and removal of heavy metal species in aquatic environments is of continued interest to address ongoing efforts in water security. This study was focused on the preparation and characterization of aniline grafted chitosan (CS-Ac-An), and evaluation of its adsorption properties with Cu(II) under variable conditions. Materials characterization provides support for the grafting of aniline onto chitosan, where the kinetic and thermodynamic adsorption properties reveal a notably greater uptake (>20-fold) of Cu(II) relative to chitosan, where the adsorption capacity (Qm) of CS-Ac-An was 106.6 mg/g. Adsorbent regeneration was demonstrated over multiple adsorption-desorption cycles with good uptake efficiency. CS-Ac-An has a strong fluorescence emission that undergoes prominent quenching at part per billion levels in aqueous solution. The quenching process displays a linear response over variable Cu(II) concentration (0.05–5 mM) that affords reliable detection of low level Cu(II) levels by an in situ “turn-off” process. The tweezer-like chelation properties of CS-Ac-An with Cu(II) was characterized by complementary spectroscopic methods: IR, NMR, X-ray photoelectron (XPS), and scanning electron microscopy (SEM). The role of synergistic effects are inferred among two types of active adsorption sites: electron rich arene rings and amine groups of chitosan with Cu(II) species to afford a tweezer-like binding modality.
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    Supramolecular Chemistry of Polymer-Based Molecular Tweezers: A Minireview
    (MDPI, 2024-09-14) Vafakish, Bahareh; Wilson, Lee
    Polymer-based molecular tweezers have emerged as a prominent research area due to their enhanced ability to form host–guest complexes, driven by advancements in their design and synthesis. The impact of the spacer structure on the tweezers is predominant. They can be rigid, flexible, and stimuli-responsive. Herein, a new generation of molecular tweezers is introduced as polymer-based molecular tweezers. The integration of molecular tweezers onto biopolymers has significantly expanded their potential applications, making them promising candidates, especially in drug delivery, owing to their biocompatibility, adaptive structural features, and versatile interaction capabilities. The unique structure of polymer-based molecular tweezers, particularly when integrated with biopolymers, creates a unique nano-environment that enhances their interaction with guest molecules. This minireview focuses on the synthesis and applications of polymer-based molecular tweezers and examines how the incorporation of various spacers affects their binding affinity and specificity. These features highlight the advancement of these polymer-based systems, emphasizing their potential applications, particularly in drug delivery, water treatment technology, and future research opportunities.
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    Surface-Modified Chitosan: An Adsorption Study of a “Tweezer-Like” Biopolymer with Fluorescein
    (MDPI, 2019-08-18) Vafakish, Bahareh; Wilson, Lee
    Tweezer-like adsorbents with enhanced surface area were synthesized by grafting aniline onto the amine sites of a chitosan biopolymer scaffold. The chemical structure and textural properties of the adsorbents were characterized by thermogravimetric analysis (TGA) and spectral methods, including Fourier transform infrared (FT-IR), nuclear magnetic resonance (1H- and, 13C-NMR) and scanning electron microscopy (SEM). Equilibrium solvent swelling results for the adsorbent materials provided evidence of a more apolar biopolymer surface upon grafting. Equilibrium uptake studies with fluorescein at ambient pH in aqueous media reveal a high monolayer adsorption capacity (Qm) of 61.8 mg·g−1, according to the Langmuir isotherm model. The kinetic adsorption profiles are described by the pseudo-first order kinetic model. 1D NMR and 2D-NOESY NMR spectra were used to confirm the role of π-π interactions between the adsorbent and adsorbate. Surface modification of the adsorbent using monomeric and dimeric cationic surfactants with long hydrocarbon chains altered the hydrophile-lipophile balance (HLB) of the adsorbent surface, which resulted in attenuated uptake of fluorescein by the chitosan molecular tweezers. This research contributes to a first example of the uptake properties for a tweezer-like chitosan adsorbent and the key role of weak cooperative interactions in controlled adsorption of a model anionic dye.
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    Flax fiber-chitosan biocomposites with tailored structure and switchable physicochemical properties
    (Elsevier, 2023-11-21) Mir, Mariam; Wilson, Lee D.
    A facile and sustainable synthesis of unique flax fiber composites (FFCs) is reported, where raw flax fiber (FFR) was immobilized with variable chitosan content. FFCs were structurally characterized via TGA, XRD, SEM analysis, and spectroscopy (IR, NMR, and Raman mapping). Physicochemical characterization of FFCs enabled estimation of the point-of-zero-charge (PZC), solvent swelling at variable pH. Dye adsorption with Rose Bengal (RB) and Methylene Blue (MB) afforded characterization of the surface chemistry of the materials. This contribution study is a first reported example that highlights the unique structure-property relationships of FFC materials and the role of electrostatic interactions between the pristine fiber substrate and chitosan. FFCs with incremental chitosan content display the following trends: (i) greater solvent swelling at variable pH (350 % for FFCs and ca. 100 % for FFR and commercial absorbents), (ii) two-fold enhanced adsorption of RB (FFC 0.5 to FFC 2.0) and (iii) 1.5-fold decreased adsorption of MB (FFC 2.0 to FFC 0.5). The unique “switchable” sorption properties of the FFCs toward solvent and dyes was revealed upon facile and noncovalent immobilization of chitosan onto FFR. The sustainable composites reported herein offer a potential adsorption-based technology suitable for filter-based applications in “smart textiles” to biomedical sorbents for wound healing.
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    Chitosan Biocomposites with Variable Cross-Linking and Copper-Doping for Enhanced Phosphate Removal
    (MDPI, 2024-01-16) Udoetok, Inimfon A.; Karoyo, Abdalla H.; Mohamed, Mohamed H.; Wilson, Lee D.
    The fabrication of chitosan (CH) biocomposite beads with variable copper (Cu2+) ion doping was achieved with a glutaraldehyde cross-linker (CL) through three distinct methods: (1) formation of CH beads was followed by imbibition of Cu(II) ions (CH-b-Cu) without CL; (2) cross-linking of the CH beads, followed by imbibition of Cu(II) ions (CH-b-CL-Cu); and (3) cross-linking of pristine CH, followed by bead formation with Cu(II) imbibing onto the beads (CH-CL-b-Cu). The biocomposites (CH-b-Cu, CH-b-CL-Cu, and CH-CL-b-Cu) were characterized via spectroscopy (FTIR, 13C solid NMR, XPS), SEM, TGA, equilibrium solvent swelling methods, and phosphate adsorption isotherms. The results reveal variable cross-linking and Cu(II) doping of the CH beads, in accordance with the step-wise design strategy. CH-CL-b-Cu exhibited the greatest pillaring of chitosan fibrils with greater cross-linking, along with low Cu(II) loading, reduced solvent swelling, and attenuated uptake of phosphate dianions. Equilibrium and kinetic uptake results at pH 8.5 and 295 K reveal that the non-CL Cu-imbibed beads (CH-b-Cu) display the highest affinity for phosphate (Qm = 133 ± 45 mg/g), in agreement with the highest loading of Cu(II) and enhanced water swelling. Regeneration studies demonstrated the sustainability and cost-effectiveness of Cu-imbibed chitosan beads for controlled phosphate removal, whilst maintaining over 80% regenerability across several adsorption–desorption cycles. This study offers a facile synthetic approach for controlled Cu2+ ion doping onto chitosan-based beads, enabling tailored phosphate oxyanion uptake from aqueous media by employing a sustainable polysaccharide biocomposite adsorbent for water remediation by mitigation of eutrophication.
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    Low adsorption affinity of athabasca oil sands naphthenic acid fraction compounds to a peat-mineral mixture
    (Elsevier, 2024-04-24) Meulen, Ian J. Vander; Steiger, Bernd G.K.; Asadi, Mohsen; Peru, Kerry M.; Degenhardt, Dani; McMartin, Dena W.; McPhedran, Kerry M.; Wilson, Lee D.; Headley, John V.
    Much of the toxicity in oil sands process-affected water in Athabasca oil sands tailings has been attributed to naphthenic acids (NAs) and associated naphthenic acid fraction compounds (NAFCs). Previous work has characterized the environmental behaviour and fate of these compounds, particularly in the context of constructed treatment wetlands. There is evidence that wetlands can attenuate NAFCs in natural and engineered contexts, but relative contributions of chemical, biotic, and physical adsorption with sequestration require deconvolution. In this work, the objective was to evaluate the extent to which prospective wetland substrate material may adsorb NAFCs using a peat-mineral mix (PMM) sourced from the Athabasca Oil Sands Region (AOSR). The PMM and NAFCs were first mixed and then equilibrated across a range of NAFC concentrations (5–500 mg/L) with moderate ionic strength and hardness (∼200 ppm combined Ca2+ and Mg2+) that approximate wetland water chemistry. Under these experimental conditions, low sorption of NAFCs to PMM was observed, where sorbed concentrations of NAFCs were approximately zero mg/kg at equilibrium. When NAFCs and PMM were mixed and equilibrated together at environmentally relevant concentrations, formula diversity increased more than could be explained by combining constituent spectra. The TOC present in this PMM was largely cellulose-derived, with low levels of thermally recalcitrant carbon (e.g., lignin, black carbon). The apparent enhancement of the concentration and diversity of components in PMM/NAFCs mixtures are likely related to aqueous solubility of some PMM-derived organic materials, as post-hoc combination of dissolved components from PMM and NAFCs cannot replicate enhanced complexity observed when the two components are agitated and equilibrated together.
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    Eggshell incorporated agro-waste adsorbent pellets for sustainable orthophosphate capture from aqueous media
    (Royal Society of Chemistry, 2024-04-04) Steiger, Bernd G. K.; Bui, Nam T.; Babalola, Bolanle M.; Wilson, Lee D.
    In this study, granular adsorbents containing varying ratios of torrefied wheat straw (TWS), eggshells (ES), and chitosan (Chi) were prepared, which are referred to as ternary wheat straw composites (TWCs). The TWCs were assessed for mechanical stability during handling in aqueous media and their orthophosphate (Pi) adsorption properties were studied at equilibrium. The characterization of the TWCs employed spectroscopy (IR, solids 13C NMR, PXRD), TGA, and surface area/pore size analysis via N2 gas and dye (4-nitrophenol) adsorption. The BET surface area for the composites increased with greater ES/Chi content from 0.26 m2 g−1 for C72 (80% TWS content) to 2.2 m2 g−1 for C22 (20% TWS content; 40% each ES and Chi content). The Pi adsorption properties of selected TWC adsorbents were evaluated via the Langmuir, Freundlich, and Sips isotherms at variable pH (4.5, 8.5) and 295 K. The TWCs showed moderate Pi uptake (23–30 mg g−1) at pH 4.5 with a slight decrease (9–12 mg g−1) at pH 8.5 for elevated Pi concentrations. Environmentally relevant Pi concentrations (<5 mg L−1) revealed that TWCs with 20–80% TWS content observed similar uptake (ca. 1 mg g−1). This study demonstrates that sustainable composite adsorbents that contain TWS, Chi and ES were modified to yield mechanically stable systems with tailored orthophosphate adsorption properties, especially at low concentrations for neutral or slightly alkaline pH. The proof-of-concept for this adsorbent technology reveals the role of synergistic effects, along with its overall sustainability and scalability, according to a facile synthetic strategy that includes support based on a preliminary cost analysis for these granular adsorbents.
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    Polylactic Acid Composites Reinforced with Eggshell/CaCO3 Filler Particles: A Review
    (MDPI, 2024-04-19) Homavand, Anahita; Cree, Duncan E.; Wilson, Lee D
    Statistics reveal that egg production has increased in recent decades. This growth suggests there is a global rise in available eggshell biomass due to the current underutilization of this bio-waste material. A number of different applications for waste eggshells (WEGs) are known, that include their use as an additive in human/animal food, soil amendment, cosmetics, catalyst, sorbent, and filler in polymer composites. In this article, worldwide egg production and leading countries are examined, in addition to a discussion of the various applications of eggshell biomass. Eggshells are a rich supplement of calcium carbonate; therefore, they can be added as a particulate filler to polymer composites. In turn, the addition of a lower-cost filler, such as eggshell or calcium carbonate, can reduce overall material fabrication costs. Polylactic acid (PLA) is currently a high-demand biopolymer, where the fabrication of PLA composites has gained increasing attention due to its eco-friendly properties. In this review, PLA composites that contain calcium carbonate or eggshells are emphasized, and the mechanical properties of the composites (e.g., tensile strength, flexural strength, tensile elastic modulus, flexural modulus, and elongation (%) at break) are investigated. The results from this review reveal that the addition of eggshell/calcium carbonate to PLA reduces the tensile and flexural strength of PLA composites, whereas an increase in the tensile and flexural modulus, and elongation (%) at break of composites are described herein.
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    Hydrolyzed Forms of Cellulose and Its Metal Composites for Hydrogen Generation: An Experimental and Theoretical Investigation
    (MDPI, 2024-07-06) Faye, Omar; Udoetok, Inimfon A.; Szpunar, Jerzy A.; Wilson, Lee D
    The quest for a smooth transition from fossil fuels to clean and sustainable energy has warranted studies on alternative energy materials. Herein, we report on an experimental and theoretical study focused on hydrogen generation through the hydrolysis of microcrystalline cellulose (MCC) treated in different media (deionized water, sodium hydroxide) and MCC functionalized with magnesium (MCC-Mg), titanium (MCC-Ti), and niobium (MCC-Nb). The XRD results reveal the decreased crystallinity of MCC due to ball milling along with the formation of metal oxide composites between MCC and various metals (magnesium, titanium, and niobium). Theoretical studies using NVT molecular dynamic simulations with the NH chain thermostat implemented in the Dmol3 provides further support to the experimental results reported herein. The results from the experimental and theoretical studies revealed that ball milling and composite formation with metal species enhanced the kinetics of the hydrolysis of MCC and, consequently, hydrogen generation, while the addition of NaOH and urea inhibited the hydrogen yield.
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    Synthesis of Conjugated Polymers: Comparing the Indophenine Reaction with Traditional Methods
    (American Chemical Society, 2024-07-10) Berbigier, Jônatas Faleiro; Kelly, Timothy L.
    Conjugated polymers are an important class of materials whose development underpins many recent advances in organic electronics. Traditionally, these polymers have been synthesized by transition metal-catalyzed cross-couplings using organometallic reagents (e.g., Stille couplings). Although direct heteroarylation polymerization (DHAP) dispenses with the organometallic intermediates, DHAP is still a metal-catalyzed coupling, requiring both catalyst optimization and purification to remove trace metal contaminants. In contrast, a recent report from our group demonstrated that the indophenine reaction can be used as a metal-free method to prepare conjugated polymers; however, from this initial proof-of-concept study, it was not clear how it compared to other methods of conjugated polymer synthesis. Therefore, in this report, we synthesized the same polymer using three distinctly different approaches: Stille coupling, DHAP, and the indophenine reaction. This allows us to directly compare the three methodologies; we find that each offers distinct trade-offs in terms of atom economy, defects, and molecular weight.
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    Effect of a Fluorinated Surfactant on Langmuir Monolayer Properties of Minimal-Linker Gemini Surfactants
    (Elsevier B.V., 2024-07-08) Singh, Srikant K.; Paige, Matthew F.
    A new class of carboxylic acid-terminated gemini surfactants which contain the smallest possible headgroup linker (a single bond) has recently been reported in the literature. In this current work, we have explored how Langmuir monolayers of two different alkyl tail chain length variants (n = 12, n = 16) of these surfactants, dubbed Cn-0-Cn, are impacted by mixing with a benchmark perfluorinated surfactant, perfluorotetradecanoic acid (PF). Pure PF and C16-0-C16 monolayers share similar general characteristics, yielding compact, incompressible, solid-like films at the air-water interface. In contrast, the shorter tail chain variant, C12-0-C12 forms expanded, compressible liquid-like films. While both tail chain variants formed mixed films with PF that were generally expanded in comparison with their pure components, and were also phase-separated, the extent of interactions between film components and the resulting micron-scale morphology of the mixed films were different for the two alkyl chain lengths. Overall, PF induces different packing behavior in both the systems and the observations are attributed to the difference in the dispersion forces originating from the tail chain length differences.
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    Probing the Formation and Evolution of Pd Nanoparticles on the Surface of γ-Al2O3 using a Pd(II) Coordinating Polymer as a Precursor: An in-situ X-ray Scattering and Spectroscopy Study
    (American Chemical Society, 2024-06-26) Singh, Siddhant; Scott, Robert W.J.
    Due to the small size and very low metal loadings in heterogeneously supported nanoparticle catalysts, it is a characterization challenge to trace and control the formation and structural evolution of nanoparticles during their synthesis. In this report, we have probed the formation of alumina-supported Pd nanoparticles by thermal treatment of a 1:3 composite of a Pd(II) coordination polymer (Pd(II)-CP) and a γ-Al2O3 powder using in situ X-ray total scattering and X-ray absorption spectroscopy. By comparing the pyrolysis process of Pd(II)-CP in the absence and presence of γ-Al2O3, we found that the sintering of Pd nanoparticles by the coalescence of nucleation sites can be significantly reduced on γ-Al2O3 surfaces. The introduction of γ-Al2O3 provides far better control over the size, distribution, and speciation of the synthesized Pd nanoparticles. The results showed that the sintering of Pd nanoparticles does not occur on the surface of γ-Al2O3 until the Pd(II)-CP structure is fully collapsed at 400 °C, most likely because the organic framework of Pd(II)-CP provides spatially distinct sites for Pd nucleation. Moreover, the interface of the γ-Al2O3 surface and Pd(II)-CP protected the Pd nanoparticle nucleation sites from air oxidation up to 500 °C. Thereafter, a slow conversion of the Pd fcc phase to the PdO phase started taking place, which was facilitated by the formation of an amorphous PdOx phase as an intermediate.
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    Making chemical sense of phase in soft X-ray spectroptychography
    (Elsevier, 7/12/2023) Joseph, Stitsky; Jian, Wang; Stephen, Urquhart
    Spectroptychography is being used to realize a significant improvement in the spatial resolution of x-ray spectromicroscopy, allowing chemical microanalysis at finer spatial scales. The chemical sensitivity of near edge X-ray absorption fine structure (NEXAFS) is familiar to most researchers who use x-ray spectromicroscopy for chemical microanalysis. However, the additional phase information available through ptychography provides additional and tantalizing data, and potentially additional chemical information. This paper explores the chemical information available in phase for a system of silicon dioxide nanospheres.
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    Coal-Based Activated Carbon via Microwave-Assisted ZnCl2 Activation for Methyl Violet 2B Dye Removal: Optimization, Desirability Function, and Adsorption Mechanism
    (MDPI, 2023) Musa, Salis A.; Abdulhameed, Ahmed Saud; Baharin, Siti Nor Atika ; ALOthman, Zeid; Wilson, Lee; Jawad, Ali H.
    In this work, activated carbon (referred to as MCAC) was produced by microwave radiation assisted ZnCl2 activation using Malaysian coal (MC) as a precursor. The Brunauer–Emmett–Teller findings indicate that the MCAC has a relatively large surface area (798.18 m2/g) and a mesoporous structure (average pore diameter of 3.67 nm). The removal of Methylene Violet (MV 2B) a cationic dye model, was employed to investigate the adsorption properties of MCAC. A numerical desirability function in the Box–Behnken design (BBD) was employed to optimize the independent crucial adsorption variables as follows: A: MCAC dose (0.02–0.1 g); B: pH (4–10); and C: time (5–25 min). The results of equilibrium and dynamic adsorption showed that the adsorption of MV 2B followed Freundlich and pseudo-second order models, respectively. The maximum amount of MV 2B dye that the MCAC could adsorb (qmax) was 134.1 mg/g. Electrostatic interactions, π-π stacking, H-bonding, and pore diffusion contribute to the adsorption of MV 2B dye onto the MCAC surface. This study demonstrates the potential to utilize MC as a low-cost precursor for the efficient synthesis of MAC and its utility for the removal of pollutants.
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    Electrocatalytic Oxidation of Nitrophenols via Ag Nanoparticles Supported on Citric-Acid-Modified Polyaniline
    (MDPI, 2023) Khani, Milad; Sammynaiken, Ramaswami; Wilson, Lee
    Citric-acid-modified polyaniline (P-CA) and P-CA modified with Ag nanoparticles (Ag@PCA) were prepared via an in situ reduction method. The physicochemical properties of P-CA and Ag@P-CA were compared to unmodified polyaniline (PANI) and PANI-modified Ag nanoparticles (Ag@PANI). Ag@P-CA had a lower content of aniline oligomers compared to Ag@PANI. P-CA and Ag@P-CA had a greater monolayer adsorption capacity for 2-nitrophenol and lower binding affinity as compared to PANI and Ag@PANI materials. X-ray photoelectron spectroscopy and cyclic voltammetry characterization provided reason and evidence for the higher conductivity of citric-acid-modified materials (P-CA and Ag@P-CA versus PANI and Ag@PANI). These results showed the potential utility for the optimization of adsorption/desorption and electron transfer steps during the electrochemical oxidation of nitrophenols. The oxidation process employs Ag@P-CA as the electrocatalyst by modifying polyaniline with Ag nanoparticles and citric acid, which was successfully employed to oxidize 2-nitrophenol and 4-nitrophenol with comparable selectivity and sensitivity to their relative concentrations. This work is envisaged to contribute significantly to the selective conversion of nitrophenols and electrocatalytic remediation of such waterborne contaminants.
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    Moisture Content and Mechanical Properties of Bio-Waste Pellets for Fuel and/or Water Remediation Applications
    (MDPI, 2023) Anisimov, Yuriy A.; Steiger, Bernd; Cree, Duncan; Wilson, Lee
    The current research is focused on the mutual comparison (mechanical properties, response to humidity) of agro-waste composite materials. The purpose of this work is directed at the valorization of agro-waste biomass products and to investigate their mechanical stability for transport or other applications (in dry and wet states). Three different types of agro-waste (oat hull (Oh), torrefied wheat straw (S), and spent coffee grounds (SCG)) were blended with kaolinite (K) and chitosan (CHT) at variable weight ratios to yield ternary composites. Mechanical properties were represented by measuring hardness (in compression mode) and elastic modulus (under tension mode). Young’s (elastic) modulus was measured both for dried and hydrated samples. The pelletized materials were prepared in two forms: crosslinked (CL) with epichlorohydrin and non-crosslinked (NCL). The hardness of the Oh pellets was poor (75 N) and decreased by four times with greater agro-waste content, while crosslinking affected the hardness only slightly. S pellets had the highest level of hardness at 40% agro-waste content (160 N), with a concomitant decrease to 120 N upon crosslinking. SCG pellets had the least change in hardness for both CL and NCL specimens (105–120 N). The trends of Young’s modulus were similar to hardness. Hydration caused the elastic modulus to decrease ca. 100-fold. In general, S and SCG composites exhibit the greatest hardness and Young’s modulus compared to Oh composites (CL or NCL) in their dry state.
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    A Fixed-Bed Column with an Agro-Waste Biomass Composite for Controlled Separation of Sulfate from Aqueous Media
    (MDPI, 2023) Solgi, Mostafa; Steiger, Bernd; Wilson, Lee
    An agro-waste composite with a pelletized form was prepared and characterized via IR and 13C solids NMR spectroscopy. Thermal gravimetry analysis (TGA) was used to study the weight loss profiles, while SEM images provided insight on the biocomposite morphology, along with characterization of the sulfate adsorption properties under equilibrium and dynamic conditions. The sulfate monolayer adsorption capacity (qe = 23 mg/g) of the prepared agro-waste pellets was estimated from the adsorption isotherm results by employing the Langmuir model, and comparable fitting results were obtained by the Freundlich model. The dynamic adsorption properties were investigated via adsorption studies with a fixed bed column at pH 5.2. The effects of various parameters, including flow rate, bed height and initial concentrations of sulfate, were evaluated to estimate the optimal conditions for the separation of sulfate. The experimental data of the breakthrough curves were analyzed using the Thomas and Yoon–Nelson models, which provided satisfactory best-fits for the fixed bed kinetic adsorption results. The predicted adsorption capacities for all samples according to the Thomas model concur with the experimental values. The optimum conditions reported herein afford the highest dynamic adsorption capacity (30 mg/g) as follows: 1100 mg/L initial sulfate concentration, 30 cm bed height and 5 mL/min flow rate. The breakthrough time was measured to be 550 min. This study contributes to a strategy for controlled separation of sulfate using a sustainable biocomposite material that is suitable for fixed-bed column point-of-use water treatment systems.
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    A pyridinium-modified chitosan-based adsorbent for arsenic removal via a coagulation-like methodology
    (Royal Society of Chemistry, 2023) Venegas-García, Deysi J.; Steiger, Bernd; Wilson, Lee
    The goal of this study was to synthesize a chitosan-derived adsorbent that can be used in a coagulation– flocculation (CF) process for facile integration into existing water treatment processes. Therefore, an insoluble pyridinium-modified chitosan (Chi-Py) was prepared. Structural characterization was achieved with spectroscopy (FT-IR, 13C solids NMR, and X-ray photoelectron) methods and thermogravimetric analysis. Approximately 7% di-nitrobenzene and ca. 30% pyridinium moieties were incorporated into the chitosan framework via an adapted, moderate-temperature, Zincke reaction. The arsenic removal efficiency was evaluated by a coagulation-inspired methodology at pH 7.5, where the results were compared against CF systems such as pristine chitosan, FeCl3 and chitosan–FeCl3. The kinetic and van't Hoff thermodynamic parameters for arsenic removal were calculated. Arsenic adsorption was shown to be a spontaneous and exothermic process (ΔG = −4.7 kJ mol−1; ΔH = −75.6 kJ mol−1) with a 76% arsenic removal efficiency at 23 °C and 96% at 5 °C with a maximum effective adsorbent dosage of Chi- Py of 300 mg L−1. The adsorption process for Chi-Py followed pseudo-first order kinetics, where the pyridinium-modified chitosan adsorbent can be successfully employed similar to coagulant-like systems in conventional water treatment processes. In contrast to conventional adsorbents (1–2 g L−1), a dosage of only 300 mg L−1 was required for Chi-Py that offers greater sustainability and recycling of materials. This is contrasted with single-use conventional coagulants such as FeCl3 or binary FeCl3–chitosan CF systems.