Synthesis of bifunctional nanostructured adsorbents based on anionic/cationic clays: effect of arrangement on simultaneous adsorption of cadmium and arsenate.

The development of bifunctional hybrid materials based on natural clays and layered double hydroxide (LDH) and their application on the simultaneous adsorption of Cd(II) and As(V) was investigated in this work. Two different synthesis routes, in situ and assembly, were employed to obtain the hybrid materials. Three types of natural clays, namely bentonite (B), halloysite (H), and sepiolite (S), were used in the study. These clays are characterized by a laminar, tubular, and fibrous structural arrangement, respectively. The physicochemical characterization results indicate that the hybrid materials were formed through interactions between the Al-OH and Si-OH groups present in the natural clays, and the Mg-OH and Al-OH groups present in the LDH for both synthesis routes. However, the "in situ" route yields a more homogenous material because the LDH formation is performed on the natural clay surface. The hybrid materials showed an anion and cation exchange capacity up to 200.7 meq/100 g and an isoelectric point near 7. The arrangement of natural clay has no impact on the properties of hybrid material but influences the adsorption capacity. The adsorption of Cd(II) onto hybrid materials was enhanced in comparison with natural clays, obtaining adsorption capacities of 80, 74, 65, and 30 mg/g for 15:1 (LDH:H)INSITU, 1:1 (LDH:S)INSITU, 1:1 (LDH:B)INSITU, and 1:1 (LDH:H)INSITU, respectively. The adsorption capacities of hybrid materials to adsorb As(V) were between 20 and 60 µg/g. The 15:1 (LDH:H)INSITU sample showed the best adsorption capacity being ten folds greater than halloysite and LDH. In all cases, the hybrid materials showed a synergistic effect for Cd(II) and As(V) adsorption. The adsorption study of Cd(II) onto hybrid materials showed that the primary adsorption mechanism is cation exchange between the interlayer cations in natural clay and Cd(II) in the aqueous solution. The adsorption of As(V) showed that the adsorption mechanism is attributed to anion exchange between CO23- in the interlayer space of LDH and H2ASO4- in the solution. The simultaneous adsorption of As (V) and Cd (II) shows that, during the As(V) adsorption, there is no competition by the adsorption sites. Still, the adsorption capacity towards Cd(II) was enhanced 1.2-folds. This study ultimately revealed that the arrangement of clay has a significant influence on the adsorption capacity of the hybrid material. This can be attributed to the similar morphology between the hybrid material and natural clays, as well as the important diffusion effects observed in the system.

Pyrolysis Kinetics of Byrsonima crassifolia Stone as Agro-Industrial Waste through Isoconversional Models.

This study is aimed at the analysis of the pyrolysis kinetics of Nanche stone BSC (Byrsonima crassifolia) as an agro-industrial waste using non-isothermal thermogravimetric experiments by determination of triplet kinetics; apparent activation energy, pre-exponential factor, and reaction model, as well as thermodynamic parameters to gather the required fundamental information for the design, construction, and operation of a pilot-scale reactor for the pyrolysis this lignocellulosic residue. Results indicate a biomass of low moisture and ash content and a high volatile matter content (≥70%), making BCS a potential candidate for obtaining various bioenergy products. Average apparent activation energies obtained from different methods (KAS, FWO and SK) were consistent in value (~123.8 kJ/mol). The pre-exponential factor from the Kissinger method ranged from 105 to 1014 min-1 for the highest pyrolytic activity stage, indicating a high-temperature reactive system. The thermodynamic parameters revealed a small difference between EA and ∆H (5.2 kJ/mol), which favors the pyrolysis reaction and indicates the feasibility of the energetic process. According to the analysis of the reaction models (master plot method), the pyrolytic degradation was dominated by a decreasing reaction order as a function of the degree of conversion. Moreover, BCS has a relatively high calorific value (14.9 MJ/kg) and a relatively low average apparent activation energy (122.7 kJ/mol) from the Starink method, which makes this biomass very suitable to be exploited for value-added energy production.

Nanoclays: Promising Materials for Vaccinology.

Clay materials and nanoclays have gained recent popularity in the vaccinology field, with biocompatibility, simple functionalization, low toxicity, and low-cost as their main attributes. As elements of nanovaccines, halloysite nanotubes (natural), layered double hydroxides and hectorite (synthetic) are the nanoclays that have advanced into the vaccinology field. Until now, only physisorption has been used to modify the surface of nanoclays with antigens, adjuvants, and/or ligands to create nanovaccines. Protocols to covalently attach these molecules have not been developed with nanoclays, only procedures to develop adsorbents based on nanoclays that could be extended to develop nanovaccine conjugates. In this review, we describe the approaches evaluated on different nanovaccine candidates reported in articles, the immunological results obtained with them and the most advanced approaches in the preclinical field, while describing the nanomaterial itself. In addition, complex systems that use nanoclays were included and described. The safety of nanoclays as carriers is an important key fact to determine their true potential as nanovaccine candidates in humans. Here, we present the evaluations reported in this field. Finally, we point out the perspectives in the development of vaccine prototypes using nanoclays as antigen carriers.

Application of Orange Peel Waste as Adsorbent for Methylene Blue and Cd2+ Simultaneous Remediation.

Pollution by dyes and heavy metals is one of the main concerns at the environmental level due to their toxicity and inefficient elimination by traditional water treatment. Orange peel (OP) without any treatment was applied to effectively eliminate methylene blue (MB) and cadmium ions (Cd2+) in mono- and multicomponent systems. Although the single adsorption processes for MB and Cd2+ have been investigated, the effects and mechanisms of interactions among multicomponent systems are still unclear. Batch experiments showed that in monocomponent systems, the maximum adsorption capacities were 0.7824 mmol g-1 for MB and 0.2884 mmol g-1 for Cd2+, while in multicomponent systems (Cd2+ and MB), both contaminants competed for the adsorption sites on OP. Particularly, a synergic effect was observed since the adsorption capacity of Cd2+ increased compared to the monocomponent system. Results of desorption and adsorbent reuse confirmed that the adsorbent presents good regeneration performance. The low cost of this material and its capacity for the individual or simultaneous removal of Cd2+ and MB in aqueous solutions makes it a potential adsorbent for polluted water treatment processes.

Design and application of molecularly imprinted polymers for adsorption and environmental assessment of anti-inflammatory drugs in wastewater samples.

In this study, a series of molecularly imprinted polymers (MIPs) have been synthesized using separately diclofenac, naproxen, and ibuprofen as templates with three different polymerization approaches. Two functional monomers, methacrylic acid (MAA) and 2-vinylpyridine (2-VP), were tested and ethylene glycol dimethacrylate (EGDMA) was used as crosslinker; also, template-free polymers (NIPs) were synthesized. It was found that the MIP with the highest retention percentage for diclofenac was the one prepared by the emulsion approach and with MAA (98.3%); for naproxen, the one prepared by the bulk polymerization with MAA (99%); and for ibuprofen, the one synthesized by bulk with 2-VP (97.7%). These three MIPs were characterized by scanning electron microscopy, thermogravimetric test, Fourier transform infrared, specific area measurements, and surface charge. It was found that the emulsion method allowed particle size control, while the bulk method gave heterogeneous particles. The three evaluated MIPs exhibited thermal stability up to 300 °C, and it was observed that 2-VP confers greater stability to the material. From the BET analysis, it was demonstrated that the MIPs and NIPs evaluated are mesoporous materials with a pore size between 10 and 20 nm. In addition, the monomer influenced the surface charge of the material, since the MAA conferred an acidic point of zero charge (PZC), while the 2-VP conferred a PZC of basic character. Through adsorption isotherms, it was determined  that there is a higher adsorption capacity of the MIPs at acidic pH following a pseudo-second-order kinetic model. Finally, the MIPs were used to determine the non-steroidal anti-inflammatory drugs (NSAIDs) understudy in San Luis Potosí, México, wastewater, finding concentrations of 0.642, 0.985, and 0.403 mg L-1 for DCF, NPX, and IBP, respectively.

Elucidation of adsorption mechanisms and mass transfer controlling resistances during single and binary adsorption of caffeic and chlorogenic acids.

In this work, the potential of activated carbon to remove caffeic and chlorogenic acids in aqueous solution was investigated. The study focused on evaluating the single and binary adsorption equilibrium, as well as investigating the mass transfer resistances present during the process by applying diffusional models for a future scale-up of the process. For both compounds, the single adsorption equilibrium was studied at pH values of 3, 5, and 7. The experimental adsorption isotherms were interpreted using the Langmuir and Freundlich models, obtaining maximum adsorption capacities of 1.33 and 1.62 mmol/g for caffeic and chlorogenic acid, respectively. It was found that the adsorption mechanisms for both compounds were derived from π-π, electrostatic, and H-bonding interactions. Also, the binary adsorption equilibrium was performed, and the experimental data were interpreted using the extended multicomponent Langmuir model. The results evidenced that the binary adsorption of caffeic acid and chlorogenic acid is antagonistic in nature. Finally, the experimental adsorption rate data were interpreted by an external mass transport model and a diffusional model, finding that the overall adsorption rate is governed by intraparticle diffusion. Moreover, the surface and pore volume diffusion mechanisms were meaningful.

Understanding mechanisms in the adsorption of lead and copper ions on chili seed waste in single and multicomponent systems: a combined experimental and computational study.

In the current work, a deep study to understand the adsorption phenomena occurring in single and multicomponent systems was conducted by using spectroscopic characterization, and computational tools. The experimental results showed that the adsorption capacity of chili seed is higher for Pb2+ (48 mg/g) than Cu2+ (4.1 mg/g) ions in single systems. However, the adsorption study in multicomponent systems provides important conclusions of the concentration effect of the metal ions, showing a significant antagonistic and competitive effect of both ions under equivalent concentrations of them (qPb2+ is 56% reduced) or high concentration of Pb2+ (qCu2+ is 50% reduced). Computational results correlated well with the experimental ones and evidenced all interactions proposed from spectroscopy results, accounting for the occurrence of complexation and electrostatic mechanisms between metal ions and the surface oxygenated functional groups (hydroxyl, carboxyl, and carboxylate) onto chili seed. Chemistry quantum descriptors supported the reactivity behavior of the chemical species implicated. All results evidenced that Pb2+ and Cu2+ adsorption on chili seed surface is governed by the occurrence of combined ionic exchange, π-interaction, complexation, and electrostatic attraction.

Simultaneous removal of metronidazole and Pb(II) from aqueous solution onto bifunctional activated carbons.

In this work, it was analyzed the behavior of three commercial activated carbons with different textural and chemical properties to adsorb individually metronidazole and lead ions from aqueous solution. Afterwards, the activated carbons were modified with citric acid to remove both compounds simultaneously. Both sets of activated carbons were characterized chemically and texturally. XPS analysis was performed to corroborate the adsorption mechanism of lead on the surface of the carbons. Finally, the intraparticle diffusion of both adsorbates was elucidated by the application of diffusional model in three dimensions. The results evidenced that adsorption mechanism for MNZ and Pb(II) is independent, the adsorption for MNZ is governed by π-π dispersive interactions, whereas Pb(II) adsorption is mainly controlled by electrostatic interactions. The binary adsorption equilibrium shows that the adsorption of MNZ is independent from the concentration of Pb(II), whereas the adsorption of Pb(II) is affected by the presence of MNZ at low concentrations (0.1 mmol L-1), but it remains almost constant at concentrations of MNZ between 0.1 and 1.5 mmol L-1. Finally, the mass transport of MNZ was faster than Pb(II) from the solution to the external surface of activated carbon and the mass flux of MNZ inside the particle was superior to the mass flux of Pb(II). Lastly, there might be an obstruction phenomenon with MNZ impeding Pb(II) to reach the active sites placed into the carbon's microporosity structure. Graphical abstract.

Antagonistic, synergistic and non-interactive competitive sorption of sulfamethoxazole-trimethoprim and sulfamethoxazole­cadmium (ii) on a hybrid clay nanosorbent.

The competitive sorption of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) and SMX-Cd(II) on a hybrid clay nanosorbent (NanoSorb) was investigated in detail in this work. NanoSorb was synthesized by sorbing a surfactant on bentonite. Besides, the sorption of SMX on the NanoSorb was confirmed by FTIR analysis, and SMX was mainly sorbed on NanoSorb by a partition mechanism due to hydrophobic interactions. Otherwise, the single adsorption of Cd(II) and TMP onto NanoSorb were due to electrostatic interaction and hydrophobic partition, respectively. The capacity of NanoSorb for sorbing single SMX was very similar to that for single Cd(II), but more than 10 times higher than that for single TMP. The competitive sorption of SMX-TMP was antagonistic because the sorption of one antibiotic on NanoSorb was decreased by the presence of the other antibiotic. The uptake of SMX was reduced up to 43.4% by the presence of TMP, whereas the presence of SMX decreased the uptake of TMP up to 29.6%. The non-modified Langmuir multicomponent isotherm (NLMI) interpreted quite well the experimental competitive sorption data of SMX-TMP. On the other hand, the competitive sorption of SMX-Cd(II) on NanoSorb revealed that the sorption of SMX was non-interactive because it was not influenced by the presence of Cd(II). Whereas, the sorption of Cd(II) was synergistic or cooperative since the uptake of Cd(II) sorbed increased considerably with the uptake of SMX sorbed on NanoSorb. The two-site Langmuir model fitted the experimental competitive sorption data of Cd(II) on NanoSorb saturated with SMX. The application of this isotherm was based on the fact that Cd(II) sorbed on two types of sites: a) cationic sites of the NanoSorb and b) Pi-cation interactions between the aromatic ring of the SMX sorbed on NanoSorb and Cd2+.

Seed-Mediated Growth of Ag@Au Nanodisks with Improved Chemical Stability and Surface-Enhanced Raman Scattering.

Bimetallic Ag@Au nanoparticles (NPs) have received significant research interest because of their unique optical properties and molecular sensing ability through surface-enhanced Raman scattering (SERS). However, the synthesis of Ag@Au core-shell plasmonic nanostructures with precisely controlled size and shape remained a great challenge. Here, we report a simple approach for the synthesis of bimetallic Ag@Au nanodisks of about 13.5 nm thickness and different diameters through a seed-mediated growth process. The synthesis involves the conformal deposition of Au atoms at the corner sites of Ag nanoplate (AgNPL) seeds coupled with site-selective oxidative etching of AgNPL edges to generate Ag@Au nanodisks. The resultant Ag@Au nanodisks manifest significantly improved chemical stability and tunable localized surface plasmon resonance from the visible to the near-infrared spectral range. Moreover, in comparison to AgNPLs, the Ag@Au nanodisks showed greatly enhanced SERS performance with an enhancement factor up to 0.47 × 105, which is nearly 3-fold higher than that of the original AgNPLs (0.18 × 105). Furthermore, the Ag@Au nanodisks show a high sensitivity for detecting probe molecules such as crystal violet of concentration as low as 10-9 M and excellent reproducibility, with the SERS intensity fluctuation less than 12.5%. The synthesis route adapted for the controlled fabrication of Ag@Au nanodisks can be a potential platform for maneuvering other bimetallic plasmonic nanostructures useful for plasmonics and sensing applications.

Nanoemulsion Formulations of Fungicide Tebuconazole for Agricultural Applications.

Tebuconazole (TBZ) nanoemulsions (NEs) were formulated using a low energy method. TBZ composition directly affected the drop size and surface tension of the NE. Water fraction and the organic-to-surfactant-ratio (RO/S) were evaluated in the range of 1-90 and 1-10 wt %, respectively. The study was carried out with an organic phase (OP) consisting of an acetone/glycerol mixture containing TBZ at a concentration of 5.4 wt % and Tween 80 (TW80) as a nonionic and Agnique BL1754 (AG54) as a mixture of nonionic and anionic surfactants. The process involved a large dilution of a bicontinuous microemulsion (ME) into an aqueous phase (AP). Pseudo-ternary phase diagrams of the OP//TW80//AP and OP//AG54//AP systems at T = 25 °C were determined to map ME regions; these were in the range of 0.49-0.90, 0.01-0.23, and 0.07-0.49 of OP, AP, and surfactant, respectively. Optical microscope images helped confirm ME formation and system viscosity was measured in the range of 25-147 cP. NEs with drop sizes about 9 nm and 250 nm were achieved with TW80 and AG54, respectively. An innovative low-energy method was used to develop nanopesticide TBZ formulations based on nanoemulsion (NE) technology. The surface tension of the studied systems can be lowered 50% more than that of pure water. This study's proposed low-energy NE formulations may prove useful in sustainable agriculture.