João P. de Mesquita

Preparation of activated carbons from coffee husks utilizing FeCl3 and ZnCl2 as activating agents

Ferric chloride was used as a new activating agent, to obtain activated carbons (AC) from agro industrial waste (coffee husks). This material was compared with two samples from the same raw material: one of them activated by using the classical activating agent, zinc chloride, and the other, activated with a mixture of the two mentioned activating agents in the same mass proportion. The carbonaceous materials obtained after the activation process showed high specific surface areas (BET), with values higher than 900 m(2)g(-1). It is interesting to observe that the activation with FeCl(3) produces smaller pores compared to the activation with ZnCl(2). An important fact to emphasize in the use of FeCl(3) as activating agent is the activation temperature at 280 degrees C, which is clearly below to the temperature commonly employed for chemical or physical activation, as described in the bibliography. All the studied materials showed different behaviors in the adsorption of methylene blue dye and phenol from aqueous solutions.

Bio-based nanocomposites obtained through covalent linkage between chitosan and cellulose nanocrystals

Bio-based nanocomposites were obtained through covalent linkage between cellulose nanocrystals (CNCs) and the natural polymer chitosan (CH). The CNCs were first functionalized with methyl adipoyl chloride (MAC) and the reactive end groups on the surface of the CNCs were reacted with the amino groups of the CH biopolymer in an aqueous medium. The functionalized CNCs and the resulting nanocomposites were characterized using FTIR, TEM, XRD, and elemental analyses. Characterization of the functionalized CNCs showed that up to 8% of the hydroxyl groups in the nanocrystals were substituted by the MAC residue. The covalent linkage between the CNCs and CH was confirmed by FTIR spectroscopy. The nanocomposites demonstrated a significant improvement in the mechanical performance and a considerable decrease in the hydrophilicity relative to the neat chitosan. The approach used in this work can be extended to other natural polymers.

Hybrid layer-by-layer assembly based on animal and vegetable structural materials: multilayered films of collagen and cellulose nanowhiskers

Layer-by-layer (LBL) assembly was used to combine crystalline rod-like nanoparticles obtained from a vegetable source, cellulose nanowhiskers (CNWs), with collagen, the main component of skin and connective tissue found exclusively in animals. The film growth of the multilayered collagen/CNW was monitored by UV-Vis spectroscopy and ellipsometry measurements, whereas the film morphology and surface roughness were characterized by SEM and AFM. UV-Vis spectra showed the deposition of the same amount of collagen, 5 mg m−2, in each dipping cycle. Ellipsometry data showed an increment in thickness with the number of layers, and the average thickness of each bilayer was found to be 8.6 nm. The multilayered bio-based nanocomposites were formed by single layers of densely packed CNWs adsorbed on top of each thin collagen layer where the hydrogen bonding between collagen amide groups and OH groups of the CNWs plays a mandatory role in the build-up of the thin films. The approach used in this work represents a potential strategy to mimic the characteristics of natural extracellular matrix (ECM) which can be used for applications in the biomedical field.

A hole inversion layer at the BiVO4/Bi4V2O11 interface produces a high tunable photovoltage for water splitting

The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.

Oxidized few layer graphene and graphite as metal-free catalysts for aqueous sulfide oxidation

Few layer graphene and natural graphite were chemically modified by oxidation with HNO3 at 80 and 140 °C and used to promote the oxidation of sulfide ions in aqueous solutions. TEM, potentiometric titration, XRD, BET and Raman spectroscopy show that HNO3 treatment even at 140 °C did not modify the graphene and graphite morphologies but produced significant amounts of different oxygen surface groups. The presence of these groups on few layer graphene and graphite strongly increased the Saq2− oxidation, showing activities comparable to a high surface area activated carbon with a similar amount of oxygen surface groups. The obtained results suggest that the sulfide oxidation efficiency requires a balance between two important effects, i.e. the presence of oxygen functionalities to initiate the Saq2− oxidation and the electrical conductivity that is important to further transfer the electrons removed from sulfide.

A novel floating photocatalyst device based on cloth canvas impregnated with iron oxide

In this paper an innovative and versatile design for a catalytic photoreactor is presented. The photoreactor is based on a floating Polypropylene non-woven fabric canvas (NWF) impregnated with particles of a mixture of iron oxides and oxyhydroxides adhered to the surface of microfibers. The canvas was characterized with different techniques including Mossbauer spectroscopy, Raman scattering, FTIR, and SEM. UV-Vis spectroscopy showed that the impregnated particles presented an average gap of 2.2 eV. The activity and efficiency of the photocatalyst was tested by photodegradation of rhodamine-B (Rh-B) and the results showed that the floating photocatalyst has a high catalytic activity and maintains its efficiency even after five reuse tests at intervals of 90 min with a small average residual concentration of 6.2% Rhodamine-B in each reuse cycle.

A perspective of mitochondrial dysfunction in rats treated with silver and titanium nanoparticles (AgNPs and TiNPs)

Nanotechnology is a growing branch of science that deals with the development of structural features bearing at least one dimension in the nano range. More specifically, nanomaterials are defined as objects with dimensions that range from 1 to 100 nm, which give rise to interesting properties. In particular, silver and titanium nanoparticles (AgNPs and TiNPs, respectively) are known for their biological and biomedical properties and are often used in consumer products such as cosmetics, food additives, kitchen utensils, and toys. This situation has increased environmental and occupational exposure to AgNPs and TiNPs, which has placed demand for the risk assessment of NPs. Indeed, the same properties that make nanomaterials so attractive could also prove deleterious to biological systems. Of particular concern is the effect of NPs on mitochondria because these organelles play an essential role in cellular homeostasis. In this scenario, this work aimed to study how AgNPs and TiNPs interact with the mitochondrial respiration chain and to analyze how this interaction interferes in the bioenergetics and oxidative state of the organelles after sub-chronic exposure. Mitochondria were exposed to the NPs by gavage treatment for 21 days to check whether co-exposure of the organelles to the two types of NPs elicited any mitochondrion-NP interaction. More specifically, male Wistar rats were randomly assigned to four groups. Groups I, II, III, and IV received mineral oil, TiNPs (100 μg/kg/day), AgNPs (100 μg/kg/day), and TiNPs + AgNPs (100 μg/kg/day), respectively, by gavage. The liver was immediately removed, and the mitochondria were isolated and used within 3 h. Exposure of mitochondria to TiNPs + AgNPs lowered the respiratory control ratio, causing an uncoupling effect in the oxidative phosphorylation system. Moreover, both types of NPs induced mitochondrial swelling. Extended exposure of mitochondria to the NPs maintained increased ROS levels and depleted the endogenous antioxidant system. The AgNPs and TiNPs acted synergistically-the intensity of the toxic effect on the mitochondrial redox state was more significant in the presence of both types of NPs. These findings imply that the action of the NPs on mitochondria underlie NP toxicity, so future application of NPs requires special attention.