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Sensors and biosensors play a key role as an analytical tool for the rapid, reliable, and early diagnosis of human diseases. Such devices can also be employed for monitoring environmental pollutants in air and water in an expedited way. More recently, nanomaterials have been proposed as an alternative in sensor fabrication to achieve gains in performance in terms of sensitivity, selectivity, and portability. In this direction, the use of cellulose nanomaterials (CNM), such as cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), has experienced rapid growth in the fabrication of varied types of sensors. The advantageous properties are related to the supramolecular structures that form the distinct CNM, their biocompatibility, and highly reactive functional groups that enable surface functionalization. The CNM can be applied as hydrogels and xerogels, thin films, nanopapers and other structures interesting for sensor design. Besides, CNM can be combined with other materials (e.g., nanoparticles, enzymes, carbon nanomaterials, etc.) and varied substrates to advanced sensors and biosensors fabrication. This review explores recent advances on CNM and composites applied in the fabrication of optical, electrical, electrochemical, and piezoelectric sensors for detecting analytes ranging from environmental pollutants to human physiological parameters. Emphasis is given to how cellulose nanomaterials can contribute to enhance the performance of varied sensors as well as expand novel sensing applications, which could not be easily achieved using standard materials. Finally, challenges and future trends on the use of cellulose-based materials in sensors and biosensors are also discussed.

Biosensors are analytical tools that can be used as simple, real-time and effective devices in clinical diagnosis, food analysis, and environmental monitoring. In the last years, electrospun nanofiber's engineering has emerged as a possible strategy to improve the performance of biosensor devices. These nanostructures present a high surface-to-volume ratio, interconnected porous structure, low barrier to diffusion, and adjustable surface functionality. Additionally, nanofibers have also been demonstrated to work efficiently as platforms to immobilize biomolecules, providing a suitable microenvironment to biologically active molecules, which is beneficial for biosensing performance. This review aims to highlight the different strategies (e.g., adsorption, covalent binding, entrapment, and imprinting) for immobilizing functional receptors onto nanofibers surface for the development of specific and sensitive (bio)chemical assays, which can be used for a wide range of applications. The attractive features of electrospun nanofibers and the biorecognition elements properties are also presented and discussed. Finally, the current challenges and future opportunities for the design of nanofiber-based biosensing interfaces are also addressed.

Hydrogen peroxide (H2O2) is an important compound for several industrial sectors, but it becomes harmful to human health under high concentrations. Thus, the development of simple, low cost and fast analytical methods capable to detect and monitor H2O2 is fundamentally important. In the present study, we report a simple route for synthesizing silver nanoparticles (AgNPs) in the presence of a nanostructured polysaccharide (cellulose nanowhiskers) to produce a hybrid material, which was employed as a colorimetric probe for H2O2 detection. Our results revealed that AgNPs tend to experience catalytic decomposition when exposed to H2O2, causing a decrease of AgNPs absorption band at 410 nm in accordance with H2O2 concentration. This decrease was linearly dependent on H2O2 concentration (in the ranges 0.01–30 μM and 60–600 μM), yielding limits of detection of 0.014 μM and 112 μM, respectively. The easy-to-interpret H2O2 sensor also proved to be suitable for real samples analysis even in the presence of other interfering substances.

In this book chapter, we report the recent advances in the development and application of chemical sensors based on green composite materials for environmental analysis. Emphasis is given on the sensor performance in terms of materials employed (including macromolecules from vegetal sources combined with varied nanostructures), structure–property relationships, and device fabrication technology. Specifically, the chapter focuses on green materials obtained from vegetal biomass including cellulose, lignin, starch, alginate, pectin, and vegetal protein, indicating the viability for the construction of non-toxic, recyclable, renewable, and biodegradable devices. Firstly, a brief overview on different types of chemical sensors, including electronic tongues, electrochemical sensors, and chemical optical sensors, is presented. Then, the general aspects of green composites as sensing layers are outlined and discussed with respect to their application in environmental analytical chemistry. Emphasis is placed on results reporting the detection of heavy metals and bacterial contamination in water as wells as hazardous volatile organic compounds. Lastly, a brief perspective on the challenges and upcoming opportunities toward the development of novel sensing devices based on green composites is discussed

We report a paper-based electrochemical immunosensor made with sustainable materials to detect aflatoxin B1 (AFB1), a highly toxic, carcinogenic mycotoxin found in food. The immunosensor was prepared with a waterproof paper substrate and low-cost graphite-based conductive ink through a simple cut-printing method. The working electrode was functionalized with a drop-cast film of multiwalled carbon nanotubes (MWCNT)/chitosan on which a layer of anti-AFB1 monoclonal antibodies was immobilized covalently. The architecture of the immunosensor was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and electrochemical impedance spectroscopy (EIS), including the effective immobilization of the active layer of anti-AFB1. With EIS as the principle of detection, the immunosensor could detect AFB1 in the range from 1 to 30 ng&middot, mL&minus, 1, and detection limit of 0.62 ng&middot, 1. This sensitivity is sufficient to detect AFB1 in food according to regulatory agencies. The immunosensor exhibited good repeatability, reproducibility, stability, and selectivity in experiments with a possible interferent. Furthermore, detection of AFB1 in maize flour samples yielded recovery of 97&ndash, 99%, in a demonstration of the possible use of the paper-based immunosensor to detect AFB1 using extraction solutions from food samples.

Reliable analytical techniques to evaluate dairy products, including milk, are of outmost importance to ensure food safety against contaminants. Among possible substances employed as adulterants in milk, urea raises deep concern due to its harmful effects to consumer’s health. In the present study, a biosensing platform was developed to be applied in the electrochemical detection of urea. The sensing platform was fabricated using polymeric electrospun nanofibers of polyamide 6 (PA6) and polypyrrole (PPy) deposited onto fluorine doped tin oxide (FTO) electrodes, which were then modified with zinc oxide nanoparticles (ZnO). This material showed excellent properties for the immobilization of urease enzyme, conferring the FTO/PA6/PPy/ZnO/urease electrode high sensitivity for urea detection within the concentration range between 0.1 and 250 mg dL−1 with a limit of detection of 0.011 mg dL−1. The results achieved evidence the potential of electrospun nanofibers-based electrodes for applications in biosensors aiming at dairy products analysis.

Sensors and biosensors for monitoring food traceability, quality, safety, and nutritional value are of outmost importance nowadays. Electrospinning, a simple, straightforward and versatile technique to fabricate 1D micro- and nanomaterials, is among the most potential strategies to further advance the development of chemical (bio)sensors. Electrospun nanofibers are capable of improving several attributes of chemical (bio)sensors due to the high specific surface area, high porosity and 1-D confinement characteristics. Furthermore, the possibility to buildup multifunctional nanostructures by functionalizing the nanofiber surface with a wide range of distinct nanomaterials (such as carbon nanotubes, graphene, nanoparticles and conjugated polymers), enhances the (bio)sensing capabilities through additional properties and synergistic effects. In this review, we outline the representative progress in the last decade on the development of multifunctional hybrid electrospun nanofibers of varied morphology and composition, and their applications in chemical (bio)sensor platforms for analysis of food and agricultural products.

The development of novel graphene-based nanocomposites is a hotspot in materials science due to their unique optical, electronic, thermal, mechanical and catalytic properties for varied applications. The present work reports on the development of a graphene-based ternary nanocomposite of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), reduced graphene oxide and gold nanoparticles (PEDOT:PSS-rGO-AuNPs) for the detection of hydrogen peroxide (H 2 O 2 ). The hybrid nanocomposite showed superior electrochemical properties and higher stability compared to each individual component as electrode materials, showing a synergistic effect between PEDOT, rGO and AuNPs. The nanocomposite was obtained via a facile one-step approach and was assembly with horseradish peroxidase (HRP). The PEDOT:PSS-rGO-AuNPs-HRP modified electrode has been used for the amperometric detection of H 2 O 2 and exhibited a high sensitivity of up to 677 μA mM −1 cm −2 , with a wide linear range from 5 to 400 μM and a low detection limit of 0.08 μM (S/N = 3). This developed enzymatic biosensor showed to be highly stable and unresponsive to potentially interfering substances, and it could be used for sensing H 2 O 2 in real samples, including tap water and bovine milk samples. These enhanced sensing performance could be ascribed to the intimate contact of AuNPs onto the rough surface of the PEDOT:PSS-rGO nanocomposite, which has a high electrical conductivity and large surface area, providing it as an excellent substrate for the growth and support of nanoparticles. The method developed in this work opens up a general route to prepare a wide range of graphene-based hybrid nanocomposite films with multiple functions including sensing and biosensing.

The influence of different supporting electrolytes as well as of different current densities on RO16 dye electrochemical oxidation using BDD electrodes has been systematically studied. The RO16 azo-dye electrooxidation experiments were performed at different current densities and three different supporting electrolytes: H2SO4 0.1 mol L-1, HClO4 0.1 mol L-1 and K2SO4 0.1 mol L-1. The results showed that a higher degradation for reactive azo dye RO16 was observed for the K2SO4 (pH=10) supporting electrolyte for a current density of 100 mA cm-2. This behavior can be associated with the deprotonation effect of the dye molecule, which can facilitate breakdown of the molecule, specifically the azo bond making color removal more efficient. In addition, in this pH there is a greater amount of hydroxyl ion (OH-) available increasing the hydroxyl radical formation.

The authors have developed an electrochemical sensor for cadmium(II) that is based on the use of a conventional fluorine doped tin oxide (FTO) electrode modified with polymeric electrospun nanofibers consisting of polyamide 6 (PA6) and chitosan which were further modified with gold nanoparticles (AuNPs). The materials were characterized by infrared spectroscopy, thermal analysis (DSC and TGA), and scanning electron microscopy. The modified electrode was applied to the detection of Cd(II) by square wave voltammetry. Response is linear in the 25 to 75 μg ⋅ L−1 Cd(II) concentration range, with a detection limit of 0.88 μg ⋅ L−1. The relative standard deviations are 4.6% and 8.2% for intra- and inter-electrode measurements, respectively. Mercury(II), lead(II), and copper(II) did not significantly interfere.

Nanotechnology has provided innovative solutions to guarantee sustainable energy and maintain a clean environment for the future. In this regard, 1D nanostructured materials, such as nanofibers, are very attractive, especially for the development of economic and environmentally friendly approaches for wastewater treatment. Recently, Solution Blow Spinning (SBS) has appeared as a powerful fiber forming technique with several advantages compared to the traditional electrospinning method. Herein, we present the fabrication of composite membranes using solution blow spun poly(methylmethacrylate) nanofibers wrapped with reduced graphene oxide (PMMA-rGO) to adsorb methylene blue (MB), which is a typical dye used in the printing and dyeing industry. The dye adsorption kinetics and isotherm follow the pseudo-second-order and the Langmuir models, respectively. The π–π stacking interactions were considered to be the major driving force for the spontaneous adsorption of MB and the maximum adsorption capacity was 698.51 mg g−1 according to Langmuir fitting. The developed nanocomposite shows great potential for decolorizing dyeing wastewater aimed at industrial and environmental remediation applications.

In this work, the electrolysis of Reactive Blue 19 (RB-19, a toxic textile dye with a high half-life) using a highly non-commercial boron-doped diamond film on titanium substrate (BDD/Ti) was studied. The BDD film with a B/C ratio of 15,000 ppm, a doping level around 10 19 cm −3 and higher content of sp 3 (diamond) than sp 2 (graphite) was produced with high quality and stability. Under appropriate conditions, the electrode promoted complete decolorization of RB-19, together with 99% of TOC removal and a significant decrease in toxicity against V. fischeri . Furthermore, benzene rings, aromatic amines and naphthalene could be removed also during the electrodegradation. The decay in dye concentration followed pseudo-first order kinetics and the values of the apparent rate constant increased with increasing current density applied. In addition, the main intermediates compounds of RB-19 degradation on BDD/Ti based on HPLC–MS analysis were amino-anthraquinone, tautomers keto-enolic, hydroquinone and benzoquinone, benzoic acid, phenol and acid aliphatic, such as oxalic acid. It is concluded that electrochemical oxidation using a BDD/Ti anode represents a satisfactorily method for the removal of RB-19 in aqueous solutions.

The presence of contaminants in water is a subject of paramount importance nowadays, which can make water improper to human consumption even when these contaminants are present at very low concentrations, causing health issues and economic losses. In this work, we evaluated the performance of nanocomposites based on nylon 6,6/chitosan electrospun nanofibers modified by cellulose nanowhiskers combined with functional materials like silver nanoparticles, gold nanoparticles, and reduced graphene oxide to be used as sensing layers of an electronic tongue (e-tongue) to detect Isoborneol. This compound, found in some plants and essential oils, is used as a natural repellent and also to produce many other chemicals. Additionally, its chemical structure is related to that of 2-methylisoborneol, a critical pollutant in aqueous media. The synergism between the nanomaterials combined with electrospun nanofibers could be verified by the enhancement of the charge transference ability. Additionally, electrical capacitance data measured with the impedimetric e-tongue were treated by Principal Component Analysis (PCA), and revealed the sensing system was able to discriminate samples contaminated with Isoborneol at nanomolar concentrations. Moreover, the electronic tongue system could detect Isoborneol in real water samples under different concentrations.

Hydrogen peroxide (H

Mercury is a heavy metal highly deleterious for the environment being associated to several diseases. Thus, novel and expedite techniques capable of detecting this heavy metal in water, even at trace levels, are highly sought for human and environmental safety purposes. Here we developed a novel electrochemical sensor for detecting mercury(II) using a green hybrid nanoarchitecture composed of reduced graphene oxide (rGO), cellulose nanowhiskers (CNW) and polyamide 6 (PA6) electrospun nanofibers. Scanning transmission electron microscopy (STEM), ultraviolet-visible (UV-VIS) absorption and Fourier transform infrared (FTIR) spectroscopies and termogravimetric analysis (TGA) were employed to elucidate the morphology and composition of CNW:rGO hybrid system. The hybrid composite proved to enhance charge transference properties, which was evaluated by cyclic voltammetry (CV) experiments. Due to the excellent electrical properties of graphene, the nanocomposite (PA6/CNW:rGO) was applied in the electrochemical detection of very low concentrations of mercury in water samples, improving the sensor sensibility. Moreover, the PA6/CNW/rGO electrode demonstrated stability, high selectivity, low detection limit and wide dynamic linear range for the detection of mercury(II).

Although various processes for the removal of Reactive Black 5 (RB5) dye from textile wastewater have been studied, the degradation pathway of RB5 on boron-doped diamond (BDD) films has not been elucidated. We here report the efficient electro-oxidation of RB5 in aqueous solution using BDD/Ti electrodes and we propose a degradation route based on intermediates and byproducts identified by high performance liquid chromatography-mass spectrometry. BDD films doped with 5000 or 15,000 ppm of B were grown on Ti plates using the hot filament chemical vapor technique to produce electrodes E1 and E2, respectively. Films were evaluated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy before and after several hours of electrolysis and were shown to be of high quality and stability. Total removal of color from RB5 solution was achieved with either electrode by electrolysis at low current density (50 mA cm−2). Total mineralization of the dye solution could be attained with electrode E2 at an applied current density of 100 mA cm−2. Under these conditions, 91% of the chromatographic area associated with RB5 (monitored at 311 nm) was removed, thereby verifying cleavage of the aromatic rings of the dye. Furthermore decolorization of RB5 followed pseudo zero-order kinetics with both electrodes and the apparent rate constant was higher with electrode E2. The results obtained indicate that BDD/Ti is a promising material for the electro-degradation of RB5 since aromatic rings and chromophoric groups were ruptured during electrolysis to generate aliphatic compounds, such as oxalic acid, that can be easily converted into CO2.

An electrochemical sensor based on polymeric electrospun nanofibers of polyamide 6 (PA6)/polypyrrole (PPy) surface-modified with two forms of graphene was developed for the detection of malathion, an organophosphorus pesticide. The materials were chosen considering the electrospun nanofibers possess large surface area and porosity, while reduced graphene oxide has remarkable electrical conductivity, which is a good strategy to increase sensor sensitivity and improve the limit of detection towards the pesticide. The surface modification of nanofibers with graphene was carried out using chemically (CRGO) and electrochemically reduced graphene oxide (ERGO), in order to demonstrate how the degree of reduction of graphene oxide can influence its electrical conductivity. The influence of the reduction on the conductivity properties of graphene-based films was studied through electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The platform modified with CRGO, which presented higher electrical conductivity compared to ERGO, was used in the electrochemical detection of the pesticide malathion and exhibited a low detection limit of 0.8 ng ml−1 (S/N = 3). The results indicate that chemically reduced graphene oxide is a potential alternative for modifying electrodes surfaces designed for sensing distinct pollutants of environmental or agricultural interest.

The eletrodeposition of titanium oxide on semiconducting boron doped diamond grown on Ti substrate was investigated. Emphasis is given in the study of the influence of the doping level on BDD in the anodic hydrolysis of TiCl3 for obtaining TiO2/BDD composites. The BDD films as-grown were characterized by Raman Spectroscopy and the acceptor concentrations were evaluated around 1019 and 1021 boron atoms cm-3 for the electrode E1 and the electrode E2, respectively. Scanning electron microscopy showed that the deposits resulted in morphology composed of small grains distributed throughout the BDD surface for both electrodes. The influence of doping level showed that for E2 electrode, the deposits presented higher density with clusters at the grain faces and best uniformity of TiO2 on its surface than that for E1 electrode. This behavior may be associated to the better conductivity of the electrode E2 due to its higher boron content enhancing the titanium oxidation reaction. According the X-ray diffraction data, the rutile TiO2 crystallographic form was obtained for all the depositions.

Methyl parathion is one of the most toxic of the organophosphate insecticides. While this agent continues to be used, natural waters in agricultural areas are likely to contain significant amounts of the biocide, representing a threat to beneficial insects, freshwater organisms, birds and mammals. The electrochemical oxidation of methyl parathion in acidic medium has been studied using a boron-doped diamond (BDD)/Ti anode under galvanostatic current control. Chronoamperometry showed that significant oxidation of reference standard methyl parathion commenced at 1.8 V vs Ag/AgCl, while spectrophotometric studies revealed that the absorbance of a commercial formulation of the insecticide decayed according to time in electrolysis. Electrochemical degradation experiments were performed in a laboratory-constructed polypropylene cell in which solutions containing methyl parathion (equivalent to 60 mg L −1 ) were subjected to electrolytic treatment at different current densities (5, 10, 25, 50 and 100 mA cm −2 ). High performance liquid chromatographic analysis demonstrated that 81.2% of the insecticide was removed in 180 min at an applied current density of 100 mA cm −2 , and a compound, identified from its UV spectrum as 4-nitrophenol, was formed either as an intermediate or as a byproduct. Under these conditions, mineralization efficiency (determined by total organic carbon analysis) was 67.6%, and the toxicity of the original electrolyte against the bioluminescent bacterium Vibrio fischeri was reduced considerably by the electrochemical treatment. It is concluded that electrooxidation using BBD/Ti electrodes represents an appropriate method for the removal of methyl parathion from contaminated waters.

A study of the electrochemical degradation of profenofos in a flow reactor with electrodes comprising boron-doped diamond films deposited on titanium substrate (BDD/Ti) as anodes has been performed. The BDD films were produced at growth times of 7 and 24 h with similar B/C ratios corresponding to acceptor concentrations of around 10 20 atoms cm − 3 . The morphological and structural characteristics of the BDD/Ti electrodes were evaluated by scanning electron microscopy and Raman scattering spectroscopy. Degradation experiments were carried out with applied current densities in the range 10 to 200 mA cm − 2 and flow rates of 50 and 300 L h − 1 . The rates of degradation of profenofos were evaluated by high performance liquid chromatography and variations in total organic carbon (TOC) were monitored during the electrochemical process in order to determine the level of mineralization of organic compounds present in the electrolyte. Under the best conditions (anode comprising a BDD film deposited on titanium for 7 h and reactor operating at a flow rate of 300 L h − 1 ) more than 95% of the profenofos was degraded and approximately 87% of TOC was removed within 120 min of reaction time.

The production, characterization, and application of boron doped diamond grown on titanium substrates (BDD/Ti) are proposed in a systematic study taking into account the optimized parameters to produce high quality electrodes in a suitable doping level applied in the electrooxidation of the Brilliant Green dye. The process efficiency was analyzed as a function of the BDD doping levels as well as their sp 2 hybridization content in the film structures. A large set of sixteen BDD/Ti samples were applied in the electrooxidation experiments at constant current density of 100 mA cm − 2 , using 100 mg L − 1 of the Brilliant Green dye in K 2 SO 4 0.1 mol L − 1 solution for 300 min. The electrooxidation efficiency in the whole sample set was analyzed by UV/VIS Spectrophotometry and by Total Organic Carbon techniques considering the influence of the electrode characteristics in the degradation process. The results showed that all the electrodes were efficient in the solution discolorization and in the organic compound mineralization. However, BDD/Ti electrode with the lowest sp 2 content associated to the intermediate doping level presented the best results. A mechanist route for the dye degradation was proposed, using the normalized parameters for the best BDD electrode, from high performance liquid chromatography — mass spectroscopy analyses.

We have studied the treatment of Reactive Black 5 (RP5) and Blue 19 (RA19), which are respectively azo and anthraquinone textile dyes, by electrochemical oxidation using a non commercial boron doped diamond electrode supported on titanium metallic with a relation between B and C equal to 15,000 ppm. Pt was used as counter electrode and Ag/AgCl(sat) was the reference electrode. The variables investigated to optimize the degradation were support electrolyte concentration (0.05, 0.1 and 0.2 mol L-1 of K2SO4), temperature (25, 35 and 45 oC) and pH (2.5 and 10) by applying a current density of 75 mA cm-2. Total decolorization was observed in all electrochemical conditions studied. The highest rates of mineralization and chromatographic area removal were attained at high support electrolyte concentration due to the increase of conductivity, which caused more generation of hydroxyl radicals. RP5 was degraded at lower electrolysis time than RA19 with smaller requirement of electric charge. The mineralization rate increased in acid medium and at higher temperature since the increase in temperature favors the generation reactions of persulfate. These conditions led to the highest levels of current efficiencies and lower energy consumed.

Boron-doped diamond (BDD) electrodes have shown characteristics that differ from other conventional electrodes, and that make them an excellent electrode in the electroanalysis, in the electrosynthesis and also in the treatment of wastewater with organic compounds. In this work, two different electrodes doped with (2,000 and 15,000 ppm) were characterized by Raman Spectroscopy and by Scanning electron Microscopy (SEM). In addition, they were characterized electrochemically by cyclic voltammetry. The electroactive area was estimated according to Cottrell's equation before and after the anodic and the cathodic treatment. From the results, it was observed that the electrodes have a similar behavior in the morphology and in the homogeneity of the films. The large potential window was confirmed for both electrodes (2.5 V vs Ag/AgCl) and for the less doped electrode was obtained a larger area without any treatment while for the more doped electrode, the major area was obtained after the cathodic treatment.

The comparison of the efficiencies for boron-doped diamond (BDD) and for DSA-Cl2® type electrodes to degrade the reactive orange 16 (RO16) dye is presented. The results for the dye electrochemical degradation were investigated by spectroscopic techniques UV/VIS analysis, Total Organic Carbon (TOC), and High Performance Liquid Chromatography (HPLC). The BDD electrode showed the higher performance in the whole range of current densities studied for the color removal as well as in the mineralization of organic materials present in such dye.

Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 × 1021 atoms cm−3, respectively. The boron levels were evaluated from Mott–Schottky plots also corroborated by Raman's spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (1 1 1) and (1 0 0). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.

In this work we have studied the treatment of imazapyr by electrochemical oxidation with boron-doped diamond anode. Electrochemical degradation experiments were performed in a one-compartment cell containing 0.45 L of commercial formulations of herbicide in the pH range 3.0–10.0 by applying a density current between 10 and 150 mA cm−2 and in the temperature range 25–45 °C. The maximum current efficiencies were obtained at lower current densities since the electrochemical system is under mass transfer control. The mineralization rate increased in acid medium and at higher temperatures. The treatment was able to completely degrade imazapyr in the range 4.6–100.0 mg L−1, although the current charge required rises along with the increasing initial concentration of the herbicide. Toxicity analysis with the bioluminescent bacterium Vibrio fischeri showed that at higher pollutant concentrations the toxicity was reduced after the electrochemical treatment. To clarify the reaction pathway for imazapyr mineralization by OH radicals, LC–MS/MS analyses we performed together with a theoretical study. Ions analysis showed the formation of high levels of ammonium in the cathode. The main final products of the electrochemical oxidation of imazapyr with diamond thin film electrodes are formic, acetic and butyric acids.

Doped diamond films on titanium substrate were systematically studied by controlling their sp 2 /sp 3 hybridization as well as their boron doping levels. Samples were grown by hot filament chemical vapor deposition technique at CH 4 additions of 1, 2, 6 and 10 sccm diluted in H 2 for a total flow rate of 200 sccm. For each CH 4 concentration four doping levels were studied. The boron source was obtained from a constant flow of 40 sccm for an additional H 2 line passing through a bubbler containing the B 2 O 3 dissolved in methanol with B/C ratios of 2000, 7000, 15,000, and 30,000 B/C ppm. Scanning electron microscopy images depicted well faceted films without cracks or delaminations. The sp 2 /sp 3 ratio as “purity index” (PI) and the “growth tendency index” (GTI), associated to the TiC formation, were evaluated by Raman and X-ray spectra, respectively. GTI index was used in this work to analyze the competition between the diamond growth and TiC formation. It is also possible to associate the GTI index in terms of C/H ratio, since when this ratio is increased, the GTI index also increased. A constant GTI increase was observed as a function of CH 4 addition for the whole range of the boron doping studied. For PI, an optimized value was observed at 6 sccm of CH 4 for the doping levels higher than 2000 ppm of B/C ratio.

This work presents the production, and the characterization of Boron-doped diamond (BDD) films deposited on Titanium (Ti) substrate (BDD/Ti) with different sp2 contents. The electrooxidation of the dye Reactive Orange 16 (RO16) is studied systematically considering the sp2 bonds influence. The results for the dye electrochemical degradations were investigated by spectroscopic techniques UV/VIS analysis, Total Organic Carbon (TOC), and High Performance Liquid Chromatography (HPLC). The BDD electrode with the lowest percentage of CH4 showed the best efficiency for the aromaticity reduction, the reduction of solution color and in the analysis of the TOC. This performance was associated to its best diamond purity. This study also demonstrated that there is a compromise between the conductivity of the films and the increase of bonds sp2 type.

The electrochemical degradation of the reactive orange 16 azo-dye (RO16) using boron doped diamond (BDD) electrodes grown on titanium substrate (BDD/Ti) is presented. Two different electrodes, produced at growth times of 7 and 24 h, were used and named as E1 and E2, respectively. Both of them are highly doped, with the acceptor concentration of around 7.0 x 1020 cm-3, evaluated by the Raman spectra. The morphological and the physical characterization confirmed the best diamond purity of E2 electrode associated with its largest and well faceted grains as well as with its lowest sp2 content. This behavior was attributed to the diamond columnar growth dominance after the stead state process, observed for the films with a thickness higher than 3.0 ?m. The electrode efficiencies were studied to degrade electrochemically the RO16 dye. The results were analyzed by UV/VIS spectroscopy, by total organic carbon (TOC) and by high-performance liquid chromatography (HPLC) techniques. The electrode E2 showed the best efficiency for both, the aromaticity reduction and the azo group fracture, from UV/VIS spectra. These tendencies were confirmed by the TOC and the chromatographic measurements. The direct relationships among the BDD morphology, physical property, and performance during the degradation process were discussed.

Fotoeletrodeposicao de particulas de cobre sobre filmes de diamante dopado com boro (DDB) com diferentes niveis de dopagem foram investigadas. Enfases foram dadas no estudo da influencia do nivel de dopagem dos filmes e na eletrodeposicao fotoassistida de cobre utilizando solucoes com diferentes pHs (acido e neutro). Os filmes crescidos foram caracterizados por Espectroscopia Raman e a concentracao de portadores foi estimada por medidas de Mott-Schottky Plot. Os resultados mostraram que a deposicao de particulas de Cu sobre os filmes de DDB apresentaram maior homogeneidade nos filmes com maior dopagem (B/C=30000 ppm) quando comparados aos filmes de menor dopagem (B/C=5000 ppm). Essa diferenca na homogeneidade pode ser atribuida a melhor condutividade do eletrodo mais dopado devido a maior quantidade de boro presente neste filme, potencializando o processo de reducao do cobre. Com relacao ao meio eletrolitico (acido, neutro) utilizado nas deposicoes fotoassistidas, foi observado, em meio neutro, uma melhor eficiencia na deposicao de Cu. Este comportamento pode estar associado a menor competicao entre o H+ e o Cu2+ pelos eletrons fotogerados, uma vez que o H+ pode ser fotoeletricamente reduzido na superficie do diamante.

This work presents aspects related to production, characterization and application of boron-doped diamond (BDD) films deposited on Titanium (Ti) substrate at different doping levels. These BDD/Ti electrodes were obtained by Hot Filament Chemical Vapor Deposition (HFCVD) technique. The BDD/Ti electrodes with the dimension of (2,5 x 2,5) cm2 were prepared from H2 (99%) and CH4 (1%) gaseous mixture kept constant in the main gas line. The doping control were obtained from an additional H2 gas flux passing through a bubbler containing a solution of B2O3 dissolved in CH3OH with the B/C ratio of 2.000 and 15.000 ppm. The morphological and structural characterization was performed by Scanning Electron Microscopy (SEM), Visible Raman Spectroscopy and X-Ray Diffraction (XRD) techniques. The application of BDD/Ti electrodes for the Brilliant Green dye electrochemical oxidation was investigated by chronopotentiometry technique. Electrochemical measurements were made using a platinum mesh as a counter electrode and Ag/AgCl/KCl(sat) as the reference electrode. The electrooxidation experiments were carried out at current densities of the 100 mA cm- 2 using 100 mg L-1 of the Brilliant Green dye and K2SO4 0,1 mol L-1 as supporting electrolyte, in a total treatment time of 300 min. The degradation process was monitored by UV-spectrophotometry, Total Organic Carbon (TOC), High Efficiency Liquid Chromatografhy (HPLC) analysis, and toxicity against the Gram-negative bioluminescent marine bacterium Vibrio fischeri analysis. Concerning to the BDD morphology, the SEM images confirms that the films grown all over the Ti substrate and did not show cracks or fissures. BDD films depicted grains with a preferential (111) crystallographic orientation. Visible Raman spectroscopy confirmed the good quality of the BDD films by the presence of the narrow band at 1332 cm-1 characteristic to the diamond signature [1]. This peak decreased in intensity due to boron incorporation in diamond films. The effect of boron doping is reflected in the spectral features. There is the appearance of the two bands located at 500 cm-1 and at 1220 cm-1 attributed to B-B vibrations and B-C vibrations, respectively. X-ray diffraction showed diamond diffraction planes, assuring the material crystallinity. It was identified carbides (TiC) and hydrides (TiH) patterns in the films/substrate interface. The electrooxidation experiments were performed using galvanostat mode by applying 100 mA cm-2. The cell temperature was kept constant at 25 ºC and the system was kept under stirring. Under these experimental conditions, the results showed that the BDD/Ti electrodes were efficient in the degradation of Brilliant Green dye. The electrode of 15.000 ppm showed better efficiency for solution decolourisation as well as higher efficiency in the mineralization of organic compounds compared to those obtained for lightly doped electrode (2.000 ppm). However, the ecotoxicity tests showed the highest efficiency for the 2.000 ppm electrode. This result can be associated to the high conductivity of the 15.000 ppm electrode that may improve the secondary reactions generated through the supporting electrolyte. In this sense, the high generation of peroxodisulfate ions from these secondary reactions provides this high toxicity in the degraded solutions (Table 1). This behavior was also observed in the ecotoxicity measurements using only the supporting electrolyte. Acknowledgements: FAPESP (2010/18462-2) and CNPq (Brazil). [1] May, P. W.; Ludlow, W. J.; Hannaway, M.; Heard, P. J.; Smith, J. A.; Rosser, K. N. Diamond and Related Materials 17, (2008), 105-11.

The thiadiazolylurea derivative tebuthiuron (TBH) is commonly used as an herbicide even though it is highly toxic to humans. While various processes have been proposed for the removal of organic contaminants of this type from wastewater, electrochemical degradation has shown particular promise. The aim of the present study was to investigate the electrochemical degradation of TBH using anodes comprising boron-doped (5000 and 30 000 ppm) diamond (BDD) films deposited onto Ti substrates operated at current densities in the range 10–200 mA cm −2 . Both anodes removed TBH following a similar pseudo first-order reaction kinetics with k app close to 3.2 × 10 −2 min −1 . The maximum mineralization efficiency obtained was 80%. High-pressure liquid chromatography with UV–VIS detection established that both anodes degraded TBH via similar intermediates. Ion chromatography revealed that increasing concentrations of nitrate ions (up to 0.9 ppm) were formed with increasing current density, while the formation of nitrite ions was observed with both anodes at current densities ⩾150 mA cm −2 . The BDD film prepared at the lower doping level (5000 ppm) was more efficient in degrading TBH than its more highly doped counterpart. This unexpected finding may be explained in terms of the quantity of impurities incorporated into the diamond lattice during chemical vapor deposition.

The aim of the present study was to investigate the electrochemical degradation of sodium dipyrone in aqueous medium using a flow-by reactor equipped with anodes comprising boron-doped diamond film supported on titanium. The system was operated under electrolyte flow conditions that produced laminar (50 L h−1) or turbulent (300 L h−1) regimes in the internal section of the reactor. Spectroscopic and chromatographic analyses revealed that dipyrone was degraded completely within 120 min of electrolysis at applied potentials ⩾+4.0 V independent of the flow regime. The highest rate of removal of total organic carbon was achieved at an applied potential of +5.0 V and an electrolyte flow rate of 300 L h−1. Under these conditions, 52% of the initial organic load was removed after 2 h of electrolysis and 95.2% was eliminated after 8 h reaction. It is concluded that electrochemical technology is effective for the degradation of dipyrone and its possible products formed in aqueous medium.