Jair Freitas

• PhD
• Senior Lecturer at Federal University of Espírito Santo

This work presents an optimization of the construction, treatment, and activation of 3D-printed electrochemical sensors (E-3D). For this, was used a 2³-full factorial design examining three key variables at two levels: electrode height, electrode diameter, and printing speed. Moreover, it evaluates various physical, chemical, and electrochemical me...

Poultry litter (PL) hydrochars obtained at different temperatures and charring times were characterized by solid-state ¹H, ¹³C and ³¹P nuclear magnetic resonance (NMR) spectroscopy. ¹³C NMR spectra obtained with cross polarization (CP) and magic-angle spinning evidenced the chemical and structural changes suffered by PL during its transformation in...

Considering the environmental impact and health risks caused by oily wastewater in the petrochemical industry, it is crucial to develop more efficient separation techniques than traditional methods, such as membrane separation, for treating stable emulsions enriched with natural surfactants. This study investigated the preparation of dense cellulos...

Caffeine (CAF), present in various pharmaceutical formulations and food supplements, is one of the most consumed substances worldwide. Therefore, it is necessary to develop ways to monitor the presence and quantity of this compound in the environment and pharmaceutical industries. Thus, the present study reports the construction of a sensor that em...

Coumarins have great pharmacotherapeutic potential, presenting several biological and pharmaceutical applications, like antibiotic, fungicidal, anti-inflammatory, anticancer, anti-HIV, and healing activities, among others. These molecules are practically insoluble in water, and for biological applications, it became necessary to complex them with c...

In this work, the synthesis and structural, thermal, vibrational, morphological, and electronic characterization of 2D-like pure graphene oxide (GO) and phosphorus-containing graphene oxide (GOP) sheets were investigated. The average thicknesses of GO and GOP were 0.8 μm and 3.1 μm, respectively. The electron energy-loss spectroscopy spectra were u...

Pesticides effectively manage fungal diseases in fruits and vegetables; however, their toxicity poses significant environmental risks to human beings. Consequently, the chemical industry faces a daunting challenge in controlling or eliminating the presence of pesticides in the natural environment. The present work reports the synthesis of zeolitic...

Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can b...

The performance of several faujasite zeolites prepared under different synthesis gel conditions on the adsorption of cobalt and nickel ions is described in this work. Results of X-ray diffraction, scanning electron microscopy, N2 physisorption and solid-state 27Al/29Si nuclear magnetic resonance spectroscopy indicate that the initial synthesis gel...

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present...

Phosphorus-containing graphene-based hybrids are materials with outstanding properties for diverse applications. In this work, an easy route to produce phosphorus-graphene oxide hybrid materials is described, involving the use of variable amounts of H3PO4 and H2SO4 during the reaction of oxidation of a graphitic precursor. The physical and chemical...

Biochar-based catalysts and waste polystyrene were employed to study their effects on both the yield and composition of the oil produced on the intermediate pyrolysis of green coconut (Cocos nucifera L.) pericarp through catalytic co-pyrolysis. Biochar from intermediate pyrolysis was directly employed as a catalyst, but steam-activated biochars wit...

Many previous studies presented the effectiveness of ketoconazole (KTZ) against leishmaniasis. However, the bioavailability and therapeutic efficacy of free KTZ are limited due to its low aqueous solubility. In this study, an inclusion complex (IC6HKTZ) was prepared with p-sulfonic acid calix[6]arene (CX6SO3H) to improve the solubility and efficacy...

Herein, a novel grafted chitosan nanogel with 3,4-methylenedioxycinnamic acid was carried out aiming at the encapsulation of the monoterpenes carvacrol and thymol, with the purpose of developing a material that can be used in the control of the fungus Microsporum canis. The nanogel encapsulation efficiency showed an encapsulation capacity of 12.9%...

The advancement in the use of spectroscopic techniques to investigate coffee samples is of high interest especially considering the widespread problems with coffee adulteration and counterfeiting. In this work, the use of solid-state nuclear magnetic resonance (NMR) is investigated as a means to probe the various chemically-distinct phases existent...

The effects caused by the interaction with graphene-like layers on the 1H NMR spectra of water molecules adsorbed onto porous carbon materials were investigated by a combination of shielding calculations using density functional theory (DFT) and 1H NMR experiments. Experimental 1H NMR spectra were recorded for different water-containing carbon mate...

Biochar and ashes derived from coffee husk were used as heterogeneous catalysts in the synthesis of biodiesel through a transesterification reaction. The catalysts were obtained from the carbonization, activation, and combustion of raw coffee husks. Their properties were characterized by solid-state 13C and 31P nuclear magnetic resonance (NMR) spec...

Graphene quantum dots (GQDs) are nanosized systems that combine beneficial properties typical of graphenic materials (such as chemical stability, biocompatibility and ease of preparation from low-cost precursors) with remarkable photoluminescent features. GQDs are well-known for their low cytotoxicity and for being promising candidates in applicati...

Activated carbons containing iron compounds dispersed in their structure have shown great potential for use in advanced oxidation processes, expressively when aiming at the degradation of organic contaminants in water. In this work, we investigated the chemical and structural transformations of nanocomposites constituted by nanostructured Fe/P-cont...

The presence of microcontaminants in the water supply system offers adverse impacts. This study analyzed the performance of two powdered activated carbons (PAC1 and PAC2) in the removal of 2,4-D herbicide in ultrapure water (UW) and natural water (NW) to verify the influence of natural organic matter (NOM) on the adsorptive process. The properties...

Colocasia esculenta (taro) is traditionally reported to be rich in bioactive compounds with pharmacological properties, and it is a source of starch—a natural polymer with film-forming capacity. The present work aimed to use the crude dry extract from taro rhizome in high proportions to form polymeric films in association with PVA, for use as bioma...

The production of activated carbon using as precursor a microalgae biomass produced in a wastewater treatment plant, consisting of an Upflow Anaerobic Sludge Blanket (UASB) reactor, followed by high-rate aerobic ponds, was studied. The harvest of microalgae biomass was carried out through coagulation with Tanfloc®, flocculation and settling. Activa...

Using a coprecipitation route in aqueous medium with different precipitating agents (NH4OH and NaOH), iron-oxide nanostructures were prepared with distinct structural and magnetic properties. X-ray diffraction (XRD), ⁵⁷Fe Mossbauer spectroscopy and N2 sorption experiments indicated that the sample synthesized with NaOH had nanocrystalline goethite...

Graphene nanoflakes have attracted a growing interest owing to their tunable and unique electronic, optical, and magnetic properties. In particular, recent breakthroughs in the on-surface synthesis and characterization of graphene nanoflakes exhibiting π-magnetism have shown their promising great potential for spintronic applications. In this conte...

Environmental contamination by metal ions and water-soluble organic pollutants has become a major concern worldwide, since many industrial activities intensify the use and discharge of these substances; in fact, a few cost-effective solutions to this important issue are available to these days. In this context, the use of zeolite-based materials (n...

In this work, a new magnetic composite, with good performance in the adsorption of boron from aqueous solutions, is proposed. The composite was prepared from CoFe2O4 and MgO precursors, which were produced by the sol-gel method using orange juice residues. X-ray diffraction, scanning electron microscopy, infrared spectroscopy, ⁵⁷Fe Mössbauer spectr...

Ni metal particles, with sizes ranging from 70 to 110 nm, dispersed in activated carbon produced from the babassu coconut endocarp (BAC) were successfully synthesized and evaluated by scanning electron microscopy, dispersive energy X-ray spectroscopy, flame atomic absorption spectroscopy and powder X-ray diffraction. These hybrid BACNi-X materials...

Commercial cell-based skin regenerative products are highly expensive, carry the risk of rejection and require a long cell culture period to manufacture. This work describes the synthesis of bilayer films from poly(globalide) (PGl) and regenerated cellulose nanofibers (rCNFs) and their use as a cell-free scaffold to support keratinocyte attachment...

This letter aims to contribute to the debate around the difficulties and pitfalls with the interpretation of solid-state ¹³C nuclear magnetic resonance (NMR) spectra in graphitic materials, with special emphasis on the case of ¹³C-enriched samples and particularly dealing with the models used to fit the spectra recorded in magic angle spinning (MAS...

The hydrothermal synthesis of nano-faujasite has been successfully performed and the effects of some crystallization parameters were investigated, along with the use of this material as heavy-metal ion adsorbent. X-ray diffraction patterns have shown that the structure of the nano-faujasite is strongly dependent on both, the crystallization time an...

The photo-Fenton activity of graphitic carbon nitride (g-C3N4) has been widely studied, nevertheless, its Fenton-like catalytic behavior in the dark has not yet been demonstrated. In the present work, it is shown that oxygenated g-C3N4 obtained at different temperatures (500-600 °C) can degrade indigo carmine with hydrogen peroxide in the dark by a...

This work describes the synthesis of hybrid materials based on reduced graphene oxide (rGO) and cobalt oxide (CoO) from recycled Li-ion batteries. A hydrometallurgical route was employed in the recycling process, with citric acid and nitric acid used as the leaching agents for the cathode and anode materials, respectively. Graphene oxide (GO) was p...

Nuclear magnetic resonance (NMR) spectroscopy has been applied worldwide to study the chemical composition of lignocellulosic biomass and to analyse changes resulting from the chemical processing of these materials. In this work, solid-state ¹³C NMR was used to study the lignin contents of a large set of lignocellulosic materials derived from vario...

The discovery of new drugs and dosage forms for the treatment of neglected tropical diseases, such as human and animal leishmaniasis, is gaining interest in the chemical, biological, pharmaceutical, and medical fields. Many pharmaceutical companies are exploring the use of old drugs to establishing new drug dosage forms and drug delivery systems, i...

Eco-green biodiesel is an alternative fuel produced by a sustainable methodology and using renewable sources as feedstock due to its green nature and lower emission of pollutants in comparison with conventional fuels. In this work, biodiesels were produced using an innovative source of catalysts, a mixture of metal hydroxides: lithium-sodium (LiOH...

Activated biocarbons were prepared using biomass wastes: sugarcane bagasse, coconut shell and endocarp of babassu coconut; as a renewable source of low-cost raw materials and without prior treatments. These activated biocarbons were characterized by textural analysis, solid-state ¹³C nuclear magnetic resonance spectroscopy, X-ray diffraction and sc...

The knowledge of the different physical mechanisms determining the relaxation of the magnetization is crucial to obtain reliable petrophysical parameters from NMR experiments. Some studies have focused on asymptotic mechanisms providing simple expressions for the relaxation rate in terms of parameters of the system. The main difficulties in solving...

Catalysts containing Na and Ca compounds dispersed in a porous carbon support were prepared by a wet chemical route followed by heat treatments and their catalytic performance in the transesterification reaction of soybean oil with methanol was investigated. The chemical composition and the structural properties of the Na,Ca-based catalysts were mo...

The 13C NMR chemical shifts corresponding to different sites in atomistic models of disordered carbons were computed at different H contents by employing DFT calculations. Structural models were generated by molecular dynamics simulations and validated by the pair distribution functions; further bonding analyses were carried out to determine the am...

Different catalysts containing CaO particles dispersed in commercial activated carbon were prepared by wet impregnation followed by heat treatments. The catalytic efficiency of the prepared materials was investigated by evaluating their performance in biodiesel production by the transesterification reaction of soybean oil with methanol. The catalys...

The concentration of nitrogen compounds in crude oils is relatively low, less than 2 wt%, but these compounds are detrimental to refining processes and the environment. In particular, they can form deposits, spoil fuels, and contribute to air pollution. They are potentially carcinogenic as well. Nitrogen compounds identified in refining processes c...

The feasibility of obtaining cellulose acetate from lignocellulosic precursors is of great interest from the environmental, economic and technological points of view. Herein, sugarcane bagasse and vegetable sponge (Luffa cylindrica ) were used as precursors to produce cellulose using the organosolv extraction procedure. From the extracted cellulose...

Design of metal oxide nanoparticles is a key study for obtaining high functional materials with tunable properties. For that purpose, great progress on chemical methods for controlling the growth of the nanoparticles during the synthesis has been made. However, an important challenge faced by this field of study is to completely understand the crys...

Activated carbons are well-known porous materials as an effective adsorbent used for the removal of emerging contaminants, such as herbicides, which are increasingly present in water bodies. Most water treatment plants, specially in Brazil, are unable to completely remove such contaminants by the conventional process and advanced treatment using ac...

In this paper, we report for the first time, to the best of our knowledge, the experimental generation of dark pulses in the 1.5 µm band from a passively $Q$ -switched fiber laser employing graphite oxide as the saturable absorber, generating tunable microsecond pulses with kHz repetition rates. The graphite oxide samples were obtained by recycling...

Pseudocapacitive materials can enhance the energy storage performance of supercapacitors by making use of surface redox reactions. In recent years, different iron compounds have been investigated as pseudocapacitive materials, showing promising features for supercapacitor electrode applications. Carbon nanocomposites containing iron/phosphorus comp...

The difficulties and pitfalls with the interpretation of solid-state ¹³C nuclear magnetic resonance (NMR) spectra in graphitic materials are discussed in detail here, with special emphasis on the case of ¹³C-enriched samples, which have been used in several recent NMR studies. The issues with the spectral simulation and the interpretation of the sp...

The adsorption behavior of β-zeolite prepared with different Si/Al ratio from synthesis gel and the effect of their chemical and textural properties on the zinc, copper and cadmium ions removal from aqueous solutions are studied in this work. The samples were characterized by N2 physisorption, X-ray diffraction, X-ray fluorescence, scanning electro...

Hydrogen gas (H2) is a molecule with several applications that can be used as clean and renewable fuel to produce electrical energy through its use in fuel cells. Although H2 can be found rarely in its pure form on earth, is possible to obtain it in large quantities from the water electrolysis. In this process, the electrochemical hydrogen evolutio...

Carbon materials are widely used as supercapacitor electrodes while iron oxides and other iron compounds are promising electrode materials due to its pseudocapacitive contribution. This work deals with the preparation and electrochemical characterization of iron/carbon composites for supercapacitor electrode applications. The carbon precursor sampl...

Correlations between the photocatalytic activity and the chemical composition of carbon-supported P-Fe-based nanocomposites were found. Nanoporous carbon was prepared by chemical activation with H3PO4 of the endocarp of babassu coconut. The synthesis of the nanocomposites was conducted by aqueous impregnation of the support with Fe(NO3)39H2O and N...

The current study aimed obtaining antimicrobial sachets that could be used as preservatives for foods. Basil (BEO) and Pimenta dioica (PDEO) essential oils (EOs) were analyzed by GC-FID and GC–MS and tested against the foodborne bacteria S. aureus, E. coli, L. monocytogenes, P. aeruginosa, S. Enteritidis, and the food-spoilage mold B. nivea. Then,...

Lignocellulosic biomass has been widely studied as a source of cellulose- and related products, attracting the great interest of researchers dealing with renewable energy sources, vegetable waste recycling and biomaterials. In this work, the babassu coconut shells (epicarp and endocarp) were used for the achievement of products such as cellulose, c...

Activated biocarbons (ABs) with high specific surface area were prepared by the one-step methodology using three different agricultural biomass wastes: sugarcane bagasse (SB), coconut shell (CS) and endocarp of babassu coconut (EB). These lignocellulosic precursors are generated in large quantities in Brazil (among other countries) and, due to inap...

Scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction were successfully used to observe the location and morphology of the silica phytoliths in biomass-derived carbons and their transformation into SiC and SiO2 particles at high heat treatment temperatures (HTT). The analyses were co...

Polymeric drag reducers have been developed over many years due to the great number of practical applications. In all of them, the molecular stability is an essential requirement. Usually, polymers break down under turbulent flows, which causes a decrease in their efficiency as drag reducers. Besides that, some specific applications, in agro and bi...

Bio-oil can be converted to carbon nanostructures such as graphene, graphite-like structures, nanotubes and closed shell nanoparticles upon reaction with H2SO4 under mild conditions, i.e. 120 °C. The formation of these carbon nanostructures is discussed in terms of dehydration, condensation and aromatization processes of the complex bio-oil molecul...

Polymeric drag reducers have been developed over many years due to the great number of practical applications. In all of them, the molecular stability is an essential requirement. Usually, polymers break down under turbulent flows, which causes a decrease in their efficiency as drag reducers. Besides that, some specific applications, in agro and bi...

A study was undertaken wherein different fingermark developers were evaluated for the recovery of fingermarks from brass cartridge cases, besides the evaluation of factors such as firing effects and surface characterization of the cases. The latent fingermarks on α-brass plates, fired and unfired cartridge cases were deposited and aged for 1–14 day...

In porous systems like natural rocks, many phenomenological models have been developed in order to study the correlations between physical properties and the pore structure of these systems. The high resolution obtained with X-ray microtomography (μCT) images (micro or nanometer scales) has allowed exploring in details the complex morphology of the...

A simple and straightforward method using microwave-assisted reactions is presented for the functionalization of graphene oxide with aromatic and non-aromatic amines, notedly dibenzylamine (DBA), p-phenylenediamine (PPD), diisopropylamine (DPA) and piperidine (PA). The as-synthesized amine-functionalized graphene oxide materials (amine-GO) were cha...

Naphthenic acids (NAs), present in a typical Brazilian acid crude oil and its thermal degradation products, were investigated using two separation methodologies: solid phase extraction (SPE) and liquid-liquid extraction (LLE). Fractions produced were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR) and negative-ion mode elec...

In this study, a new method was developed to quantify cocaine and some adulterants (lidocaine, caffeine, phenacetin, procaine and benzocaine) using the nuclear magnetic resonance spectroscopy without the use of deuterated solvents (No-D qNMR). The No-D qNMR presents as main advantages: low cost (in comparison to the use of deuterated solvents), non...

Hydrocarbons present in saturated fractions of crude oils can be assessed by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as ionizing reagents in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). In this work, five paraffin standards of different average molar mass distributions (Mw) were easily...

Activated carbons with well-developed microporosity and containing dispersed nanostructured phosphorus compounds were produced by the chemical activation with H3PO4 of an abundant Brazilian lignocellulosic residue (endocarp of babassu coconut). The chemical nature of the phosphorus-containing species in the produced materials was studied by ¹H, ¹³C...

The influence of the structural and microstructural characteristics of graphitic precursors on the production of graphite oxide (GO) is investigated in the present work. Six different graphitic precursors were used to produce GO following a modified Hummers method, namely: natural graphite, commercial lubricant graphite, milled graphite, graphite f...

In this study, cobalt (Co) was recycled from spent lithium ion batteries (LIBs) and used to synthesize cobalt ferrite (CoFe2O4-LIBs), which was applied as a catalyst for heterogeneous photo Fenton reactions that discolored methylene blue (MB) dye. The co-precipitation method was used to synthesize CoFe2O4-LIBs and CoFe2O4-R nanoparticles with spine...

The extraction and refining process of unconventional oils, including heavy and extra heavy oils, has been a challenge to be overcome in the petrochemical industry. These oils typically comprise polar compounds responsible for some undesirable properties, such as naphthenic acids (NAs), which can be associated with the high corrosion rates in refin...

The capability of a mixture of okra fiber and mucilage as drag reducer in high Reynolds number flows through a pipeline, in which the flux is maintained by a centrifugal pump with controlled rotation, is analyzed. A DR close to the maximum drag reduction asymptote, which is obtained for polymeric additives, was achieved when concentrations around 1...

The shielding tensor in 13C nuclear magnetic resonance (NMR) offers important information about the structural aspects of carbon materials from a local point of view. Not only the symmetry of the carbon site but also the presence of local structural distortions can affect the values of the isotropic shielding constant, the shielding anisotropy and...

Asphaltenes are defined as the petroleum fraction insoluble in n-alkanes and soluble in aromatic solvents as toluene. Such definition implies that asphaltenes are not a homogeneous material but a mixture of fractions. Asphaltenes represent one of major contributors to several problematic issues for the petroleum industry. Destabilized asphaltenes c...

This work describes the production and characterization of carbon-iron nanocomposites obtained from the decomposition of iron pentacarbonyl (Fe(CO)5) mixed with different carbon materials: a high surface area activated carbon (AC), powdered graphite (G), milled graphite (MG), and carbon black (CB). The nanocomposites were prepared either under argo...

Structural and magnetic properties of nanocomposite, consisting of Fe2P particles dispersed in a porous carbon matrix, have fully been investigated using X-ray diffraction, Mössbauer and ac and dc magnetization measurements. Besides production of the nanocomposite, using an activated carbon (prepared by chemical activation of a char with H3PO4), im...

Solid-state ¹³ C nuclear magnetic resonance (NMR) spectroscopy was used in this work to analyze the physical and chemical properties of plasma blacks and carbon deposits produced by thermal cracking of natural gas using different types of plasma reactors. In a typical configuration with a double-chamber reactor, N 2 or Ar was injected as plasma wor...

This work describes the production and characterization of cellulignins from vegetable waste, along with an evaluation of their performance in gasification processes. The first part of the project consists in the preparation of cellulignins from sugar cane bagasse and rice husks. The second involves the physicochemical characterization of these cel...

The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at 13 C nuclei in a ferromagnetic carb...

The structural and chemical transformations occurring in alumina-carbon composites upon heat treatment were investigated by using a combination of X-ray diffraction (XRD) and solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy. Two different carbon precursors were employed: a commercial activated carbon and a char obtained by carbonizati...

Naphthenic acids are recognized as the main corrosive species in acidic crude oils, although they represent less than 3 wt%. Alternative methods have been developed in an attempt to remove naphthenic acids from the oil, however, their implementation in petrochemical industry still represents a challenge. Herein, a sub-product of the steel industry,...

In order to investigate the interaction between single vacancies in a graphene sheet, we have used spin-polarized density functional theory (DFT). Two distinct configurations were considered, either with the two vacancies located in the same sublattice or in different sublattices, and the effect of changing the separation between the vacancies was...

Introduction The conversion of organic compounds to solid carbon materials is a complex process, which includes a variety of chemical reactions, involving many intermediate stages [1]. Greinke and Lewis [2] studied the carbonization of naphthalene, observing pitch, mesophase and coke formations, mainly through polymerizations with the loss of hydro...