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Amperometric sensing of chemical oxygen demand at glassy carbon and silicon electrodes modified with boron-doped diamond
Abstract
A boron-doped diamond (BDD) sensor is proposed for effective detection of chemical oxygen demand (COD) by means of amperometric technique. Boron-doped diamond thin films, acting as active sensors, were deposited on both silicon wafer and glassy carbon (GC) substrates by microwave plasma assisted chemical vapour deposition. SEM micrographs showed that BDD–Si displays triangle-faceted crystallites ca. 0.5–3 μm in size, while BDD–GC has triangle-faceted crystallites ranging from 0.5 to 3 μm and also a small amount of square-faceted grains 0.5–1 μm in size. The structure of BDD was confirmed by broad Raman bands centred at 483 cm−1 and 1216 cm−1. Cyclic voltammograms were measured in tetrabutylammonium perchlorate/dimethyl sulfoxide solution to determine chemical oxygen demand by amperometric technique. The reduction of oxygen at boron-doped diamond predominantly involves the one electron reduction of oxygen to superoxide. The reduction of oxygen on BDD–Si and BDD–GC was found to be quasi-reversible (ΔE = 59 − 100 mV). The lowest detection limit was about 0.9 mg l−1. Two different types of electrochemical behaviour were observed at BDD–Si and BDD–GC electrodes which indicates a complexity of electroreduction of oxygen on the BDD surface
... Diamond is a wide band gap semiconductor with E g = 5.45 eV, but it can be easily doped with boron using an in situ Chemical Vapour Deposition (CVD) process. Due to the presence of boron, diamond effectively changes its electrical conductivity [12,13] and becomes a p-type semiconductor material. Such a material has remarkable electrochemical features, i.e. chemical stability [14], a wide electrochemical window [15] and high anodic stability [16]. ...
... Boron-doped diamond films are commonly used as an electrode material in the applications related to hazardous organic compounds or sensing [12,16,17]. Moreover, due to the biocompatibility of BDD, it is a great material for sensing various kinds of proteins or DNA [18,19]. ...
... The medium intensity bands in the Raman spectra of B-NCD films attributable to (a) diamond lattice at 1330-1333 cm À1 , and (b) nanocrystalline diamond at 1126-1136 cm À1 were registered. Moreover, the differences in boron content in samples can be confirmed by the growth of the band at 1231 cm À1 and a decrease in signal intensity above 1650 cm À1 , which is typical for a highly borondoped CVD diamond [12]. The D band at 1346 cm À1 can be assigned to the mixture of amorphous sp 2 and sp 3 carbon, while the G band at 1556-1558 cm À1 , to sp 2 amorphous carbon. ...
... La demanda química de oxígeno (DQO) es un parámetro que representa la cantidad de oxígeno (mg O 2 /L) consumido durante procesos de oxidación química de sustancias orgánicas y es empleado generalmente para medir el grado de contaminación del agua 1,2 . La determinación tradicional de la DQO por el método de oxidación ácida con dicromato de potasio, presenta desventajas como: interferencias por la presencia de sustancias inorgánicas susceptibles de ser oxidadas (sulfuros, sulfitos, yoduros, cloruros, etc.), tiempos de análisis relativamente largos (~ 3 h), precisión del método alrededor de 10 % y necesidad de una infraestructura, personal calificado y reactivos apropiados de un laboratorio de calidad de aguas [3][4] . ...
... Usando luego la ley de Faraday (4), 2 3 = (4) 4 (4) donde Q es la carga (Coulombios), n los moles de electrones transferidos, F la constante de Faraday (96485 C/mol) y V el volumen de reacción (L). Luego, despejando de (4) la concentración del compuesto orgánico se obtiene (5): 17 onde Q es la carga (Coulombios), n los moles de electrones transferidos, F la constante de araday (96485 C/mol) y V el volumen de reacción (L). ...
The chemical oxygen demand (COD) was determined using an electrochemical method based on electrolysis in a thin layer condition. Miniaturized electrodes of screen-printed graphite modified by PbO2-Bi electrodeposition were used for the application of exhaustive electrolysis in samples with volume in the order of microliters. The COD calibration protocol was established on the basis of the electrical charge transferred during electrolysis of standard solutions of organic compounds of interest. The response was evaluated with respect to the concentration of potassium hydrogen phthalate used as standard, the electrode potential, the concentration of chloride ions as typical interference, and the response of a typical industrial effluent. Experimental conditions were identified for high precision determinations with deviations of 5 % in all cases, and relative error between 1 and 6 %. The proposed method is capable of reproducing exact and accurate values of COD, when compared to the traditional method based in oxidation with H2SO4 and K2Cr2O7, demonstrating that electrochemical oxidation under thin layer condition, is a convenient method to determine the COD of aqueous solutions.
... Based on Gaussian-fitted peaks, the I D /I G at the non-hydrogenated carbon surface was estimated to be 1.78, which was improved to 2.2 and 2.7 at triethylsilane and phenylsilane hydrogenated carbon electrodes, respectively, with a downshift of the D peak from 1569 cm − 1 to 1565 cm − 1 compared to the non-hydrogenated counterpart. Similarly, Bogdanowicz et al. [38] reported an I D /I G ratio of 4.6 and 0.5 at borondoped diamond films deposited using plasma assisted chemical vapour deposition on silicon and glassy carbon, respectively. Their evaluation of lower I D /I G ratio at a glassy carbon was that this layer contains much more amorphous carbon than that deposited on silicon. ...
In this work, we have applied the catalytic reduction of triethylsilane and phenylsilane to hydrogenate conical-tip carbon electrodes (~1.9 μm (standard deviation 0.97 μm; N = 10) tip diameter and ~ 8.6 μm (standard deviation 0.58 μm; N = 10) axial length) to achieve a H-terminated carbon surface. In addition to forming a hydrophobic sp³‑carbon rich surface, these two silane reduction reactions yielded siloxane dendrimers with a bulky side chain and aromatic rings, respectively. In this way, high-molecular weight, amphiphilic molecules present in a biological matrix are deterred from adsorbing on the carbon electrodes, which would otherwise lead to electrode fouling that often compromises electrochemical detection of targeted analytes. This work is focussed on the X-ray photoelectron spectroscopic study and Raman spectroscopic examination of the surface characteristics of the hydrogenated conical-tip carbon electrodes to evaluate the effectiveness of the hydrogenation procedure and to confirm the composition of the electrode surface. The results obtained then aided in validating the type of carbon formed on the hydrogenated carbon electrodes. Additionally, electrochemistry of several redox markers ([Ru(NH3)6]³⁺, [Fe(CN)6]³⁻ and anthraquinone 2,4-disulfonic acid) were also used to evaluate the surface characteristics of these hydrogenated carbon electrodes.
... The recorded working potential window is 2.6 V and 3.1 V for 10k and 0.5k electrodes, respectively. The slightly narrower potential window is due to higher carrier concentration in the higher doped electrode (Bogdanowicz et al., 2013a). The EIS spectra (Fig. 3 b) includes a semicircular region which represents the electron-transfer-limited process. ...
Polyfluorinated alkyl substances (PFASs) may reach landfill leachates (LLs) due to improper waste management. In this study perfluorooctanoate (PFOA) and perfluorooctane sulphonate (PFOS) were used as representatives of PFASs in the decomposition on boron-doped diamond electrodes (BDDs) with high (10k ppm) and low (0.5k ppm) boron doping concentrations. The result shows that although better COD removal efficacies are obtained on the low-doped BDD (59 % after 8 h), the decomposition rate of PFOA and PFOS was not affected by boron doping. In LLs, at the current density of 75 mA/cm², averaged removal efficiencies of 80 % and 78 % were achieved for PFOA and PFOS, respectively. But besides concentration of mother compounds, the presence of intermediates during electrolysis should be monitored. After 8 h of LL electrolysis, the presence of long-chain degradates C6 F13 and C6 F13 COO˗ was still observed only in 10k BDD-PFOA assays, while during 0.5k assays C 6F13 and C6 F13 COO˗ form more intesively at the beginning of the process. This indirectly confirms the more intensive generation of perfluoroalkoxy and hydroxyl radicals and higher susceptibility to electrolysis of PFOA’s long-chain intermediates on 0.5k BDD. This is the first study reporting BDD-electrolysis as promising in PFAS removal from the complex matrix of LLs, despite the oxidation of competing LLs components.
... The boron doped diamond provides other unique properties that make it an ultra-sensitive electroanalytical platform for electrochemi cal sensing [9][10][11], biosensing [12,13], and electrocatalysis [14][15][16]. As an electrode material, diamond provides a wide electrochemical potential window from −1.25 V to +2.3 V SHE (standard hydrogen electrode) in aqueous electrolytes [17,18], as well as high anodic stability [19], chemical inertness, [20,21] and biocompatibility. [22,23] Besides the electrochemical performance, the high transparency of thin CVD diamond films over the whole region from the ultraviolet to the far-infrared spectral region allows for novel technological applications to optical coatings, [24,25] optoelectronic switching devices, [26] or high-speed near-infrared photodetectors. ...
In the following work we describe preparation and the electrochemical performance of thin and free-standing heavy boron-doped diamond (BDD) nanosheets. The investigated foils were deposited on Ta substrate using microwave plasma-enhanced chemical vapor deposition technique (MPECVD). Foils of two B-dopant densities were investigated, obtained on the base of 10 k and 20 k ppm [B]/[C] ratio in the gas admixture. The obtained foils can be easily peeled from substrate in deionized water to be then attached to other material, in this case poly-dimethylsiloxane (PDMS). We have shown that the top surface and the bottom side of investigated boron-doped diamond nanosheet possess significantly altered morphology and physico-chemical properties, revealed by electron microscopy, Raman spectroscopy and electrochemistry. The voltammetric response of investigated BDD foils as working electrodes indicates the highest activity for the nanosheet with higher dopant concentration, in particular on its top surface. Furthermore, electrodes are characterized with altered kinetics, characteristic for partially blocked electrodes with quasi-reversible charge transfer.
... Numerous efforts have been made to overcome these disadvantages by developing simple and rapid analytical approaches [10,11,14]. Emerging techniques for COD determination include electrochemical, chemical, photocatalytic, ultraviolet, fluorescence, chemiluminiscence, and photoelectrochemical methods [12,[15][16][17][18][19][20][21][22]. Electrochemical approaches have received much attention due to the promise of a cost effective, portable, and rapid detector with continuous monitoring abilities and little or no sample preparation. ...
... In science and technology, the diamond is known for remarkable properties such as high thermal conductivity (Sukhadolau et al., 2005), mechanical hardness, optical transparency in broad wavelength (Checoury et al., 2012;Stotter et al., 2003) or biocompatibility (Amaral et al., 2008;Bajaj et al., 2007). Natural diamond is a wide band gap semiconductor with Eg = 5.45 eV, but can be doped with boron dopant in-situ in Chemical Vapor Deposition (CVD) and becomes p-type semiconducting material (Bogdanowicz et al., 2013;Gajewski et al., 2009). Boron-doped diamond is material widely used in electrochemistry due to outstanding properties like wide electrochemical window (Iniesta et al., 2001), chemical stability even in hazardous media (Swain et al., 1998). ...
... In science and technology, the diamond is known for remarkable properties such as high thermal conductivity (Sukhadolau et al., 2005), mechanical hardness, optical transparency in broad wavelength (Checoury et al., 2012;Stotter et al., 2003) or biocompatibility (Amaral et al., 2008;Bajaj et al., 2007). Natural diamond is a wide band gap semiconductor with Eg = 5.45 eV, but can be doped with boron dopant in-situ in Chemical Vapor Deposition (CVD) and becomes p-type semiconducting material (Bogdanowicz et al., 2013;Gajewski et al., 2009). Boron-doped diamond is material widely used in electrochemistry due to outstanding properties like wide electrochemical window (Iniesta et al., 2001), chemical stability even in hazardous media (Swain et al., 1998). ...
In this chapter, fiber optic sensors based on nanolayers or thin films and their ability to perform biophotonic measurements will be presented. In the last decade, fiber optic sensors have gained popularity as biosensing devices. This has been made possible because of the design and the integration of new materials in fiber optic technology. Nanolayers and thin films made from various materials such as: nanodiamond (NCD), boron-doped nanodiamond (B-NCD), zinc oxide (ZnO), titanium dioxide (TiO2), aluminum oxide (Al2O3) and boron nitride (BN) have been successfully applied in the construction of fiber optic sensors. Nanodiamond and boron-doped nanodiamond have been synthesized by the Chemical Vapor Deposition (CVD) methods, while oxide and nitride based thin films were designed using Atomic Layer Deposition. These nanolayers and thin films have been widely used in fiber optic sensor technology as a protective coating, reflective layers and/or as a sensing medium.
... The researchers fabricated the BDD electrodes using microwave approach with further improvement to overcome the shortcomings of BDD films synthesized by the HFCVD technique. [61] They successfully synthesized the BDD films through microwave plasma enhanced chemical vapor deposition (MW PE CVD) [61] and microwave plasma assisted chemical vapor deposition (MW PA CVD), [80] and COD was then determined using the amperometric technique. These new approaches significantly decreased the detection limits (0.3 and 0.9 mg/L, respectively); however, their fabrication processes required special instruments thereby resulting in high costs. ...
Chemical oxygen demand (COD) is a critical analytical parameter for water quality assessment. COD represents the degree of organic pollution in water bodies. However, the standard analytical methods for COD are time-consuming and possess low oxidation efficiency, chloride interference, and severe secondary pollution. Works performed during the last two decades have resulted in several technologies, including modified standard methods (e.g., microwave-assisted method) and new technologies or methods (e.g., electro- and photo-oxidative methods based on advanced oxidation processes) that are less time-consuming, environment friendly, and more reliable. This review is devoted in analyzing the technical features of the principal methods described in the literature to compare their performances (i.e., measuring window, reliability, and robustness) and identify the advantages and disadvantages of each method.
... Electrochemical alternatives include amperometric detection at novel electrodes such as boron-doped diamond (BDD) (Yu et al. 2007;Yu et al. (2016) Bogdanowicz et al. 2012Bogdanowicz et al. , 2013, Cu (normal electrocatalytic type) (Silva et al. 2009), nanoparticulated Cu (Yang et al. 2011), and chronocoulometry at Ti/TiO 2 electrodes (Ge et al. 2016). ...
Water quality assessment typically includes the determination of chemical oxygen demand (COD) by oxidation of organic matter with Cr(VI) in an acidic medium followed by digestion. Unfortunately, the required reagents are harmful and the reaction times are rather long. We investigated earlier the use of H2O2 as a more environmentally friendly oxidizing agent to replace the hazardous chromates. In the present study, we have furthered this possibility by incorporating the use of H2O2 in the presence of UV light. A protocol has been devised and tested with standards and real samples that replaces toxic Cr(VI), halves the amount of silver sulfate required, and greatly reduces the necessary reaction time, thus yielding a faster and more environmentally sound method.
... The relative surface area coverage was obtained by multiplying the number of crystallites by their surface area. A similar approach was previously reported by Bogdanowicz et al. [80]. ...
There is an urgent need for an effective and economically viable increase in electrochemical performance of boron-doped diamond (BDD) electrodes that are used in sensing and electrocatalytic applications. Specifically, one must take into consideration the electrode heterogeneity due to nonhomogenous boron-dopant distribution and the removal of sp2 carbon impurities saturating the electrode, without interference in material integrity. In this work, authors describe a detailed study on electrochemical performance and the enhancement of electrochemical active surface area in the BDD electrodes that have been pretreated via chemical-assisted mechanical lapping.
The effect of lapping on both surface chemistry and oxidation processes at the BDD surface was assessed by means of chronovoltammetry, instantaneous impedance monitoring, and X-Ray photoelectron spectroscopy. Next, atomic force microscopy and scanning electron microscopy were employed to produce data on spreading resistance and surface geometry, respectively.
While the analyzed interactions are very complex and multi-level, authors suggested that the main observed effect was due to the removal of non-diamond carbon impurities from the electrode surface, decreased grain size, and heterogeneous conductivity. Short-duration pretreatments were found to be an effective route towards more efficient surface activation with negligible alterations in the diamond film structure. A prolonged pretreatment led to a decrease in grain size and lowered contribution of (111) and (110) facets, which in turn influenced the electrode kinetics.
... Diamond is a wide bandgap semiconductor with E g = 5.45 eV but when doped with boron its becomes p-type semiconducting material with outstanding electrochemical properties [5,6]. Boron-doped diamond (BDD) films are a great electrode material that have a wide electrochemical window from -1.25 to +2.3 V in aqueous electrolytes compared to standard hydrogen electrode (SHE) [7,8], high anodic stability [9], chemical stability in harsh environments [10,11], and biocompatibility [12,13]. These remarkable properties make BDD useful for many applications e.g. ...
This paper presents boron-doped diamond (BDD) film as a conductive coating for optical and electronic purposes. Seeding and growth processes of thin diamond films on fused silica have been investigated. Growth processes of thin diamond films on fused silica were investigated at various boron doping level and methane admixture. Two step pre-treatment procedure of fused silica substrate was applied to achieve high seeding density. First, the substrates undergo the hydrogen plasma treatment then spin-coating seeding using a dispersion consisting of detonation nanodiamond in dimethyl sulfoxide with polyvinyl alcohol was applied. Such an approach results in seeding density of 2 x 1010 cm -2 . The scanning electron microscopy images showed homogenous, continuous and polycrystalline surface morphology with minimal grain size of 200 nm for highly boron doped films. The sp3 /sp2 ratio was calculated using Raman spectra deconvolution method. A high refractive index (range of 2.0-2.4 @550 nm) was achieved for BDD films deposited at 500 ºC. The values of extinction coefficient were below 0.1 at λ=550 nm, indicating low absorption of the film. The fabricated BDD thin films displayed resistivity below 48 Ohm cm and transmittance over 60% in the visible wavelength range.
... Diamond shows unique electrical, physical, chemical and mechanical properties [1-3]. Due to its properties has many applications in electronics [2][3][4][5][6][7], MEMS [8][9][10][11], bio-sensors [12], may also act as an electromechanical sensor [13][14][15], be used for microfluidics [16] or be applied in neuron electrodes [11]. The chemical inertness of the polycrystalline boron doped diamond (BDD) combined with its high thermal conductivity, mechanical strength and electrical conductivity, makes it an attractive material for harsh environment applications. ...
The polycrystalline boron doped diamond (BDD) shows stable electrical properties and high tolerance for harsh environments (e.g. high temperature or aggressive chemical compounds) comparing to other materials used in semiconductor devices. In this study authors have designed electronic devices fabricated from non-intentionally (NiD) films and highly boron doped diamond structures. Presented semiconductor devices consist of highly boron doped structures grown on NiD diamond films. Fabricated structures were analyzed by electrical measurements for use in harsh environment applications. Moreover, the boron-doping level and influence of oxygen content on chemical composition of diamond films were particularly investigated. Microwave Plasma Enhanced Chemical Vapour Deposition (MW PE CVD) has been used for thin diamond films growth. Non-intentionally doped diamond (0 ppm [B]/[C]) films have been deposited on the Si/SiO2 wafers with different content of carbon, boron and oxygen in the gas phase. Then, the shape of the highly doped diamond structures were obtained by pyrolysis of SiO2 on NiD film and standard lithography process. The highly doped structures were obtained for different growth time and [B]/[C] ratio (4000 - 10000 ppm). The narrowest distance between two highly doped structures was 5pm. The standard Ti/Au ohmic contacts were deposited using physical vapour deposition for electrical characterization of NiD/BDD devices. The influence of diffusion boron from highly doped diamond into non-doped/low-doped diamond film was investigated. Surface morphology of designed structures was analyzed by Scanning Electron Microscope and optical microscope. The resistivity of the NiD and film was studied using four-point probe measurements also DC studies were done.
... It is known that carbon coatings, including diamond-like carbon (DLC) can be used in biomedical applications [7]. Moreover, so called "non-active" anodes such as boron doped diamond (BDD) electrodes could be used effectively in electrochemical sensors [3,8], designed for environment monitoring and biomedical applications [9][10]. ...
Interferometry is a desirable method for in-situ measurement of thin, dielectric film growth, as it don't modify conditions of film deposition. Here we present interferometrical measurements of thickness of doped diamond films during Chemical Vapor Deposition (CVD) process. For this purpose we used a semiconductor laser with a 405nm wavelength. Additional ex-situ measurement using spectral interferometry and ellipsometry have been performed. We found that doping diamond with boron does not cause degradation of interference of light inside the film. To our knowledge, this is the first study of optical monitoring of boron doped, polycrystalline diamond films deposition.
... These properties include, e.g., optical transparency in a broad wavelength range [8,9], chemical stability [10] and biocompatibility [7,11]. Moreover, the properties of diamond films can be easily tuned, i.e., in situ doping during the chemical vapour deposition (CVD) process effectively changes their electrical conductivity [12,13]. Diamond is also known for its high hardness. ...
... The electrodes of this type have a good chemical and electrochemical stability even in highly aggressive media, a long lifetime and a wide potential window for the water discharge. They could be used effectively in electrochemical sensors [10,11] designed for environment monitoring and biomedical applications [12,13]. They also offer an extremely high detection sensitivity of 10 -6 ÷ 10 -9 M in case of bioanalytes (e.g. ...
Abstract A conductive boron-doped diamond (BDD) grown on a fused silica/quartz has been investigated. Diamond thin films were deposited by the microwave plasma enhanced chemical vapor deposition (MW PECVD). The main parameters of the BDD synthesis, i.e. the methane admixture and the substrate temperature were investigated in detail. Preliminary studies of optical properties were performed to qualify an optimal CVD synthesis and film parameters for optical sensing applications. The SEM micro-images showed the homogenous, continuous and polycrystalline surface morphology; the mean grain size was within the range of 100-250 nm. The fabricated conductive boron-doped diamond thin films displayed the resistivity below 500 mOhm cm-1 and the transmittance over 50% in the VIS-NIR wavelength range. The studies of optical constants were performed using the spectroscopic ellipsometry for the wavelength range between 260 and 820 nm. A detailed error analysis of the ellipsometric system and optical modelling estimation has been provided. The refractive index values at the 550 nm wavelength were high and varied between 2.24 and 2.35 depending on the percentage content of methane and the temperature of deposition.
... The trends in roughness and refractive index were taken from our previous studies based on Raman spectroscopy and AFM/SEM measurements [19,20]. Deconvolution of Raman spectra gives the sp 3 /sp 2 ratio which can be used for refractive index trend estimation, while AFM/SEM results in grain size distribution supply information about the roughness variation. ...
In situ monitoring of the thickness of thin diamond films during technological processes is important because it allows better control of deposition time and deeper understanding of deposition kinetics. One of the widely used techniques is laser reflectance interferometry (LRI) which enables non-contact measurement during CVD deposition. The authors have built a novel LRI system with a 405 nm laser diode which achieves better resolution compared to the systems based on He-Ne lasers, as reported so far. The system was used for in situ monitoring of thin, microcrystalline diamond films deposited on silicon substrate in PA-CVD processes. The thickness of each film was measured by stylus profilometry and spectral reflectance analysis as a reference. The system setup and interferometric signal processing are also presented for evaluating the system parameters, i.e. measurement uncertainty, resolution and the range of measurable film thickness.
... The recent use of BDD electrodes tends to be very effective in dissolution of various organic pollutants [4,5] including ionic liquids678, phenols [9], organic solvents [10], dyes [11] as well as in disinfection [12]. It is possible because BDD has a wide electrochemical window from -1.25 to +2.3V compared to standard hydrogen electrode (SHE) [13,14]. Due to high O 2 overvoltage and the large amount of adsorbed hydroxyl radicals [@BULLETOH], oxidation processes on BDD are very dynamic as well as they affect many organic components (see Eq. (1)). ...
In this study the efficiency of electrochemical oxidation of aromatic pollutants, such as reactive dyes, at boron-doped diamond on silicon (Si/BDD) electrodes was investigated. The level of [B]/[C] ratio which is effective for the degradation and
mineralization of selected aromatic pollutants, and the impact of [B]/[C] ratio on the crystalline structure, layer conductivity and
relative sp3/sp2 coefficient of a BDD electrode were also studied. The thin film microcrystalline electrodes have been deposited on highly doped silicon substrates via MW PE CVD. Si/BDD electrodes were synthesized for different [B]/[C] ratios of the gas phase.
Mechanical and chemical stability of the electrodes was achieved for the microcrystalline layer with relatively high sp3/sp2 band
ratio. Layer morphology and crystallite size distribution were analyzed by SEM. The resistivity of BDD electrodes was studied using four-point probe measurements. The relative sp3/sp2 band ratios were determined by deconvolution of Raman and X-ray photoelectron spectra. The efficiency of degradation and mineralization of the reactive azo dye rubin F-2B was estimated based on
the absorbance measurements at 545 nm. The influence of commonly used electrolytes NaCl and Na2SO4 on the dye removal
efficiency was also investigated. The results suggest that, in general, the oxidation occurs indirectly at the anode through generation of hydroxyl radicals •OH, which react with the dye in a very fast and non-selective manner. In NaCl electrolyte the dye was also
decomposed by more selective, active chlorine species (Cl2, HOCl). However the efficiency of this process in BDD depended on
the electrode's doping level. Higher amounts of dopant on the surface of BDD resulted in the higher efficiency of dye removal in both electrolytes.
Chemical oxygen demand (COD) is an important indicator of the degree of organic pollution in water. However, the development of integrated and batch COD electrochemical sensors has always been challenging. In this study, a three-electrode integrated electrochemical sensor for the measurement of COD in surface water was evaluated. Using microfabrication with a microelectromechanical system (MEMS), the sensor was mass-produced and integrated with boron-doped diamond (BDD), Pt, and Ag/AgCl electrodes on the chip. The determination of glucose in optimal conditions provided a linear range from 5 to 200 mg L⁻¹, a detection limit of 3.899 mg L⁻¹, and satisfactory linearity (R²) of 0.998. As the sensor was fabricated by MEMS technology, good reproducibility was experimentally verified with relative standard deviations less than 4%, which suggests mass production of the sensor. The sensor was calibrated to be relatively stable in the presence of Cl⁻ and NO2⁻. A low-cost, miniature (6 mm²), and stable COD sensor was designed using microfabrication technology that may be mass-produced to build a water quality detection network in the Internet of Things era.
Asian Journal of Organic & Medicinal Chemistry
Chemical oxygen demand (COD) is one of the most significant parameters in water-quality analysis, such as wastewater effluent monitoring. However, COD determination faces challenges of long measuring time and the use of toxic substances. In this work, an Al/SnO2-TiO2 composite film electrode was prepared using the sol-gel method and dip-coating method for electrochemical determination of COD. The electrocatalytic reaction kinetics of the different organic substances on the electrode was studied in a three-electrode system. It was observed that the electrocatalytic reactions of all tested organic compounds on the Al/SnO2-TiO2 electrode fitted the first-order kinetics. Based on the reaction rate constants at different temperatures, the activation energies for electrocatalytic oxidations of methylene blue and rhodamine B were 9.92 kJ/mol and 14.7 kJ/mol, respectively. It was confirmed that dynamic behaviors of different organic substances on the electrode surface were different from each other. In addition, seven single-component organic solutions, four two-component organic solutions, and three three-component organic solutions were selected as the target standard solutions for the COD measurement experiments. Initial working currents measured by chronocoulometry were taken as the index of the value of COD of the target solutions within the operating voltage range of 1.5∼3.5 V (vs. SCE). In the range of 20∼100 mg/L, COD values of either single-component or multiple-component solutions were linearly related to the initial working currents. For solutions composed of different organic compounds with the identical COD concentration, each of their initial working currents was different from the others and increased with the working voltage. It could be concluded that the initial working currents measured by chronocoulometry was depended on COD concentration, applied voltage, as well as the composition of the tested solutions. By comparing the COD measurement results, using potassium hydrogen phthalate solution as the simulated wastewater, of the presented method with those of the standard potassium dichromate method, the accuracy and reproducibility of this method had also been approved. Therefore, we report a simple, rapid, and environmentally friendly COD determination method using an Al/SnO2-TiO2 electrode, which is feasible for single- and multiple-component organic solutions.
Portable, rapid, and cost-effective detection of environmental contamination remains an important challenge in the field of water quality analysis. Herein, we described a smartphone-based water quality monitoring system that allowed for the quantification of Pb²⁺ ions and chemical oxygen demand (COD) at an exact location. The system was composed of four main parts: (i) a whole-copper electrochemical sensor, (ii) a hand-held detector, (iii) a smartphone installed with a custom application program, and (iv) a Cloud map website. The sensor chips were made of low-cost copper, including microfabricated Cu working electrodes, Cu counter electrodes, and Cu/CuCl2 reference electrodes. The hand-held detector (∼50 g) can perform several types of electroanalytical techniques, including chronoamperometry, cyclic voltammetry, linear sweep voltammetry, and square wave voltammetry. With an Application (App), the smartphone was used to control the detector and visualize the testing results in real time. A Cloud map website was used to receive and display the contamination concentrations and geographic locations for public sharing and viewing. Since the smartphone-based system is cost-effective, small in size, field-portable, and fully wireless, it shows great potential for applications in resource-limited settings.
The main subject of this study are molecular structures and optical properties of boron-doped diamond films with [B]/[C] ppm ratio between 1000 and 10 000, fabricated in two molar ratios of CH 4 -H 2 mixture (1 % and 4 %). Boron-doped diamond (BDD) film on the fused silica was presented as a conductive coating for optical and electronic purposes. The scanning electron microscopy images showed homogenous and polycrystalline surface morphology. The Raman spectroscopy confirmed the growth of sp ³ diamond phase and sp ² carbon phase, both regular and amorphous, on the grain boundaries, as well as the efficiency of boron doping. The sp ³ /sp ² ratio was calculated using the Raman spectra deconvolution method. A high refractive index (in a range of 2.0 to 2.4 at λ = 550 nm) was achieved for BDD films deposited at 700 °C. The values of extinction coefficient were below 1.4 at λ = 550 nm, indicating low absorption of the film
To overcome the shortcomings of the conventional potassium dichromate method (PDM) for monitoring chemical oxygen demand (COD) of waters, many efforts have been made on developing quick and environment-friendly techniques. Among all alternatives, electrochemical (EC) techniques are very competitive due to their relatively simple devices and quickness. A number of electrodes have been fabricated to investigate electrochemical determination of COD. However, little work has been reported on Ti/TiO2 based electrode for this purpose. In the present work, Ti/Ti/TiO2 electrode was simply prepared by anodic oxidation of pure titanium. Aqueous solutions of potassium hydrogen phthalate and phenol were electrolyzed by chronocoulometry in a three-electrode system with Ti/Ti/TiO2 as working electrode (anode). Organic compounds were electrochemically oxidized on Ti/Ti/TiO2 electrode by hydroxyl radicals and the released electrons were recorded and transferred to currents. The electric currents were proportional to the COD values of the water samples being investigated. Based on data of COD values and corresponding currents, a linear regression equation was obtained for a certain kind of waste water. With the regression equation, current of an unknown water sample was transferred to its COD value. Conditions for the presented EC method were set up as cell voltage 2.0V v.s. SCE and pH 7.0. The linear range of COD was of about 25~530 mg/L. COD values of real waste water samples were measured by Ti/Ti/TiO2 electrode and the relative errors were all in the range of ±8% compared with data determined by conventional PDM. The electrochemicalmethodology was successfully applied to evaluate COD in waste water.
Fabrication processes of thin boron-doped nanocrystalline diamond (B-NCD) films on silicon-based micro- and nano-electromechanical structures have been investigated. B-NCD films were deposited using microwave plasma assisted chemical vapour deposition method. The variation in B-NCD morphology, structure and optical parameters was particularly investigated. The use of truncated cone-shaped substrate holder enabled to grow thin fully encapsulated nanocrystalline diamond film with a thickness of approx. 60 nm and RMS roughness of 17 nm. Raman spectra present the typical boron-doped nanocrystalline diamond line recorded at 1148 cm−1. Moreover, the change in mechanical parameters of silicon cantilevers over-coated with boron-doped diamond films was investigated with laser vibrometer. The increase of resonance to frequency of over-coated cantilever is attributed to the change in spring constant caused by B-NCD coating. Topography and electrical parameters of boron-doped diamond films were investigated by tapping mode AFM and electrical mode of AFM–Kelvin probe force microscopy (KPFM). The crystallite–grain size was recorded at 153 and 238 nm for boron-doped film and undoped, respectively. Based on the contact potential difference data from the KPFM measurements, the work function of diamond layers was estimated. For the undoped diamond films, average CPD of 650 mV and for boron-doped layer 155 mV were achieved. Based on CPD values, the values of work functions were calculated as 4.65 and 5.15 eV for doped and undoped diamond film, respectively. Boron doping increases the carrier density and the conductivity of the material and, consequently, the Fermi level.
Here we report on a novel, rapid, and environmentally friendly methodology for the determination of chemical oxygen demand (COD) using an electrochemically reduced nanoporous TiO2 electrode. A highly ordered nanoporous structure is grown directly onto a Ti plate through a three-step anodic oxidation process. Subsequent to electrochemical reduction, the nanoporous TiO2 electrode demonstrates a significant enhancement in photoelectrocatalytic activity. An advanced photoelectrochemical method based on the reduced nanoporous TiO2 is successfully developed and employed to quantify COD values in both synthetic and actual wastewater samples. Specifically, a typical processing period of 1-2 min, a practical detection limit of 8 mg L-1, and a linear range of 20-250 mg L-1 COD are achieved. More importantly, the proposed method is in excellent agreement with the standard K2Cr2O7 COD determination technique, albeit with a more rapid analysis period. Further merits include the negation of the necessity of any toxic (Cr2O7-) and highly corrosive (H2SO4) reagents, simple and automatic operation, and environmental compatibility.
Platinum nanoparticles (PtNPs) and 4-aminobenzoic acid (4-ABA) were used to modify nitrogen-doped diamond-like carbon (N:DLC) film electrode by electrodeposition and cyclic voltammetry. The bare, PtNPs-, 4-ABA-, 4-ABA/PtNPs alternately-modified N:DLC film electrodes were obtained, respectively. Various analysis technologies, such as atomic force microscopy, X-ray photoelectron spectroscopy and micro-Raman spectroscopy, have been used to study surface morphology, chemical composition and bonding structure of the film electrodes. Linear sweep voltammetry and electrochemical impedance spectroscopy were performed to study the relationship between the interfacial structure of the chemically modified N:DLC film electrodes, as well as their electrochemical sensing properties toward hydrazine sulfate. Acquired results indicate that an outermost layer modified by 4-ABA or PtNPs behaved differently.
The novel microwave pulsed-plasma based method for modification of the hydrogen-terminated polycrystalline boron-doped diamond (BDD) with thin film of polymerised allylamine (PPAAm) is reported. Modified BDD surface is resistant to hydrolysis and delamination and characterized by a high density of positively charged amino groups. The pulsed microwave plasma was applied to improve the cross-linking degree and bonding of the plasma polymeric films to boron-doped diamond. The primary amino groups of the amine-modified Si/BDD surface were coupled with antraquinone derivatives as model electroactive compounds.
Synthetized thin BDD-PPAAm films were investigated with X-Ray photoelectron spectroscopy (XPS), laser induced fluorescence (LIF) and Fourier Transform Infrared Spectroscopy (FT-IR). The FT-IR studies confirm that the molecular structure of deposited layer reproduces the monomer structure with partial transformation of amino groups into amide and nitrile. XPS results show that PPAAm film on Si/BDD electrode is electrochemically stable within range of polarization potentials between -1.1 and +1.1 V. The fluorescence properties of the PPAAm modified BDD surface makes its promising for the application as a sensors with optical readout. At the same time the electrochemical stability of the surface investigated over the wide potential range makes it an ideal for electrochemical sensors.
Surface oxidation processes play a key role in understanding electrochemical properties of boron-doped diamond (BDD) electrodes. The type of surface termination groups, which create the potential window of electrolytic water stability or hydrophobicity, influences such properties.
In this study the kinetics of oxidation process under anodic polarization were studied in situ by means of Dynamic Electrochemical Impedance Spectroscopy (DEIS) technique. This novel approach allows for obtaining the impedance data for non-stationary systems. It has been proven that for [B] dopant level of 10k ppm, polarization to 1.5 V vs. Ag|AgCl is sufficient to initiate transformation of the film terminating BDD electrodes. XPS analysis and wettability measurements confirmed oxidation under given conditions.
We report the novel modification of hydrogen-terminated polycrystalline boron-doped electrode
with microwave pulsed-plasma polymerized allylamine. BDD was coated with a very thin layer
of adherent cross-linked, pinhole- and additive-free allylamine plasma polymer (PPAAm)
resistant to hydrolysis and delamination, and characterized by a high density of positively
charged amino groups. The pulsed microwave plasma was applied to improve the cross-linking
degree and bonding of the plasma polymeric films to boron-doped diamond. The amine treated
BDD films were assessed by advanced surface analytical techniques, such as XPS, FT-IR, SEM,
laser induced fluorescence and water contact angle measurements. The amine-modified Si/BDD
surface was functionalized with selected organic molecules containing carboxylic group in the
presence of coupling agents such as diisopropylcarbodiimide (DIC). The anthraquinone
derivatives Boc-Lys(AQ)-OH, and peptide anthraquinone derivatives of dendrimere were used as
electro-active agents for characterization by cyclic voltammetry (CV). The fluorescence
reference standards Rhodamine 110 and Fmoc-Trp(Boc)-OH were selected for fluorescence
studies.
The boron-doped diamond (BDD) electrodes with different boron concentrations have been tested as electrode material for sulphamerazine (SRM) oxidation in water solution. An investigation of the electrode morphology and molecular structure was carried out using high resolution scanning electron microscopy (SEM) and Raman spectroscopy. Electro-chemical results showed clearly that the kinetics and efficiency of sulphonamide oxidation were dependent on the amount of boron incorporated in a diamond film. The mechanism of sulphonamide oxidation was also analysed by cycle voltammo-grams and by identifying oxidative species (• OH radicals) which take part in the degradation process. The aging of the material during the operation was also studied.
Nodular-cystic fat necrosis is an unusual, distinctive entity characterized by histologically en-capsulated fat necrosis in the subcutis. We report two cases of nodular-cystic fat necrosis. The lesions were subcutaneous nodules. Histopathologically, the nodules showed strong periodic acid-Schiff -positive necrotic adipose tissue with lipomembranous changes and calcification.
Development of the optoelectronic system for monitoring of diamond/DLC (Diamond-Like-Carbon) thin films growth during μPA ECR CVD (Microwave Plasma Assisted Electron Cyclotron Resonance Chemical Vapour Deposition) process is described. The multi-point Optical Emission Spectroscopy (OES) and Raman spectroscopy were employed as non-invasive optoelectronic tools. Dissociation of H2 molecules, excitation and ionization of hydrogen atoms as well as spatial distribution of the molecules became subjects of the OES investigation. The most significant parameters of the deposited film like molecular composition of the film (ratio of diamond sp3, graphite sp2 and amorphous phases), presence of defects and rate of the film growth can be investigated by means of Raman spectroscopy. Modular Raman system for in-situ monitoring of the film growth, equipped with fibre probes, was designed. Investigation with use of optoelectronic tools provides important data about CVD process progress as well as enables optimization of DLC synthesis parameters and improvement of synthesized films quality.
Boron-doped polycrystalline diamond thin films were grown over glassy carbon electrode material and POCO graphite by a microwave plasma-assisted chemical vapor deposition (CVD) using a gas mixture of methane and hydrogen. As-deposited films were analyzed by scanning electron microscopy (SEM) and Raman spectroscopy for their morphology and chemical nature, respectively the diamond films grown over glassy carbon and graphite electrode material may have some use in electroanalysis since the doped diamond films are electrically conductive, erosion resistant, and chemically inert.
Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.
In this paper low-coherence fibre-optic sensors based on the Fabry–Perot and Michelson interferometer, which
were designed and elaborated at our laboratory, are shown. We present results of investigation of the fibre-optic
sensors working in both configurations. These results allowed us to compare properties of sensors working in both
configurations. The theoretical analysis and experimental results made us possible to select best construction,
which was implemented in low-coherence fibre-optic sensors of refractive index.
The system based on spatially resolved optical emission spectroscopy dedicated for in situ diagnostics of plasma assisted CVD processes is presented in this paper. Measurement system coupled with chemical vapour deposition chamber by dedicated fiber-optic paths enables investigation of spatial distribution of species densities (Hx, H+, CH, CH+) during chemical vapour deposition process. Experiments were performed for a various gas inlet configuration at range of microwave power up to 800 W. Spatially resolved optical spectroscopy results showed that inlet configuration based on injecting hydrogen in ECR region and methane in substrate area is the most efficient for H+ and CH3+ excitation. The designed prototype of the spatially resolved optical spectroscopy system enables the high-sensitivity measurements of concentration of the species in the microwave plasma and can be used for optimisation of diamond-like carbon synthesis.
A systematic study on the morphology and electronic properties of thin heavily boron-doped nanocrystalline diamond (NCD) films is presented. The films have nominally the same thickness (≈150 nm) and are grown with a fixed B/C ratio (5000 ppm) but with different C/H ratios (0.5–5%) in the gas phase. The morphology of the films is investigated by x-ray diffraction and atomic force microscopy measurements, which confirm that lower C/H ratios lead to a larger average grain size. Magnetotransport measurements reveal a decrease in resistivity and a large increase in mobility, approaching the values obtained for single-crystal diamond as the average grain size of the films increases. In all films, the temperature dependence of resistivity decreases with larger grains and the charge carrier density and mobility are thermally activated. It is possible to separate the intra- and intergrain contributions for resistivity and mobility, which indicates that in these complex systems Matthiessen's rule is followed. The concentration of active charge carriers is reduced when the boron-doped NCD is grown with a lower C/H ratio. This is due to lower boron incorporation, which is confirmed by neutron depth profiling.
An electrochemical detection system with an F-PbO2 modified electrode for flow injection analysis to determine chemical oxygen demand (COD) was proposed and experimentally validated. The measuring principle was based on the current response on the modified electrode which was proportional to the COD value. Under the optimized experiment condition, the linear range was 100–1200 mg l−1, and the detection limit was 15 mg l−1. This method was successfully applied to determine the COD in samples without pretreatment. It was characterized by short analysis time, simplicity, low environmental impact, a limited reagent consumption and easy automation. Additionally, the COD values obtained from the proposed and conventional methods agreed well as demonstrated by the high significant correlation between the two sets of COD values (R = 0.9985, n = 25).
Electrochemical and structural characterization of glassy carbon (GC) electrodes exposed to the plasma conditions necessary to nucleate and grow diamond have been performed for the first time. The electrodes are referred to as diamond-coated (DGC) if the surface was exposed to a CH4/H-2 plasma and as hydrogenated (HGC) if the surface was exposed to only an H-2 plasma. Continuous diamond films were formed on the surfaces exposed to both plasma conditions, but due to poor adhesion, the films were easily lifted, exposing a modified GC surface. The results presented demonstrate that these modified surfaces exhibit lower voltammetric background currents and higher faradaic currents for Fe(CN)(6)(4-/3-) than does freshly polished GC. The enhanced signal-to-background (S/B) ratios lead to lower limits of detection for this redox analyte. The electrodes exhibited near-Nernstian behavior (Delta E(p) similar to 70-85 mV) for this redox analyte without any conventional surface pretreatment, and the response remained stable for long periods of time up to several weeks. The nucleation and growth mechanism of diamond on GC appears to first involve hydrogenation of the unsaturated edge plane sites on the surface, producing an sp(3) bonded ''diamond-like'' phase. These surfaces are relatively oxygen-free, as hydrogen chemisorbs at the edge plane sites, replacing the oxygen functional groups. Formation of this surface phase is followed by subsequent nucleation and growth of a diamond film. Voltammetric data for Fe(CN)(6)(4-/3-), RU(NH3)(6)(2+/3+), Fe-2+/3+, and ascorbic acid at these surfaces are presented as are structural characterization data by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and angur electron spectroscopy.
Boron-doped polycrystalline diamond thin films were grown over glassy carbon electrode material and POCO graphite by a microwave plasma-assisted chemical vapor deposition (CVD) using a gas mixture of methane and hydrogen. As-deposited films were analyzed by scanning electron microscopy (SEM) and Raman spectroscopy for their morphology and chemical nature, respectively the diamond films grown over glassy carbon and graphite electrode material may have some use in electroanalysis since the doped diamond films are electrically conductive, erosion resistant, and chemically inert.
Polycrystalline diamond thin films have been deposited on single crystal silicon substrates at low temperatures ( 600 °C) using a mixture of hydrogen and methane gases by high pressure microwave plasma-assisted chemical vapor deposition. Low temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 °C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.
The amperometric determination of chemical oxygen demand (COD) reported by Quan Xie’s group (Electrochem Commun 9:2281, 14), was a rapid, green and simple COD evaluation method. This work focused on testing and verifying this method by using a home-made boron-doped diamond (BDD) film as anode and optimizing the experiment conditions. The BDD thin film electrode was employed as anode and the electrochemical process was run with different experimental parameters including counter electrode, electrode gap, applied potential, electrolyte pH, and temperature. Standard samples were determined in the optimum conditions, a linear range of 19.2–11,600 mg l−1 COD and a low detection limit of 0.192 mg l−1 COD were well established with the present approach. The COD value of the simulated organic wastewater determined by this method agreed well with the standard dichromate method, and it showed good accuracy, stability, and reproducibility.
A simple, sensitive and environmentally friendly method was developed for determination of chemical oxygen demand (COD) by cyclic voltammetry using nickel–copper (NiCu) alloy electrode. The structure and the electrochemical behavior of NiCu alloy electrode were investigated by atomic force microscope, energy dispersive X-ray spectrometer, and cyclic voltammetry, respectively. The results indicated that NiCu alloy film with high quality was stably modified on the surface of glass carbon (GC) electrode, which could effectively oxidize a wide range of organic compounds. Subsequently, the parameters affecting the analytical performance were investigated, including pH, dissolved oxygen and concentration of chloride ion. Under optimized conditions, the linear range was 10–1533 mg L−1 and the detection limit was 1.0 mg L−1. The results obtained from the proposed method were linearly correlated to those by the classic dichromate method (r = 0.9978, p < 0.01, n = 13). Finally, the validated method was used to determine the COD values of surface water, reclaimed water and wastewater. It was shown that the proposed method had an excellent practical perspective on determination of COD in water quality control and pollution evaluation.
The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2mim][NTf2]. O2 reduction at both electrodes was found to involve the 1e− reduction of oxygen to superoxide. The formation of superoxide was verified by repeating the oxygen reduction on BDD in the presence of benzoic acid, resulting in a shift from the 1e− reduction observed in the absence of benzoic acid to a 2e− reduction yielding the hydroperoxyl anion. The reduction of O2 was found to be quasi-reversible on GC and irreversible on BDD. The significantly slower kinetics observed on the BDD electrode are likely due to the lower electronic density of states in BDD.
The paper presents analyses of the optical properties and thickness of diamond-like carbon (DLC) films deposited on oxidized silicon wafers and silicon wafers with various resistivity and different crystallographic orientations. The influence of the parameters of the radio frequency plasma-assisted chemical vapor deposition (RF PACVD) process, notably the duration of the deposition process and the negative self-bias voltage of RF-powered electrode, on the optical properties and thickness of the DLC film were investigated. These properties were determined by spectroscopic ellipsometry. To the best of our knowledge, this is the first comparative analysis of these properties for various silicon and oxidized silicon substrates. Our results show that the substrate has a significant influence on both the optical properties and the thickness of the DLC film. The differences observed are highly dependent on the discussed process parameters.
p-type {111} homoepitaxial diamond layers were grown by Microwave Plasma-Enhanced Chemical Vapor Deposition. The variation of the gas phase boron concentration led to solid-state incorporation of boron in the 6·1016–3·1021 cm−3 range. Confocal Raman spectroscopy and Raman imaging have been used to investigate this series of homoepitaxial films. As already observed for undoped or phosphorous-doped {111} epilayers, a first noticeable feature was the presence of many sharp and weak lines peaking at random in the 500–2000 cm−1 range. These peaks were all the most observed that the doping level was low. A number of boron-related Raman lines centered at about 610, 925, 1045 cm−1 were observed for solid state boron concentrations in the 1.5·1018–9·1019 cm−3 range. Above a boron concentration of 3·1020 cm−3, the usual Raman signal of heavily boron-doped diamond was recorded. The thickness of the epitaxial layers, in the 0.2–2 μm range, was too low to allow a more detailed analysis of the zone-center diamond optical phonon.
We have investigated Raman spectra of {100} and {111} facets of B-doped diamond crystals grown by microwave plasma assisted chemical vapor deposition as a function of boron concentration. We have used individual crystals rather than films to avoid stresses which can cause shifts and broadening of the Raman line. A small amount of diborane improves the crystal quality of deposited diamond with changing the Raman spectral features. The asymmetry and broadening of the one-phonon are due to Fano interference, and broad bands centered ca 500 and 1230cm−1 appear.
Diamond films were deposited on silicon substrates at 750 °C, by the hot-filament technique, from a reactive mixtures. Two wide Gaussian lines around 1330 and 1500 cm−1 with coupled variations in the whole preparation range appeared in the global Raman spectra. They were attributed to intermediate carbon defects in the diamond crystallites, which might control the confinement length of diamond phonons. Their contributions to the diamond line shift and width for all the samples is calculated and compared with the experimental results. The remaining shift is attributed to the stress (up to 1.2 GPa), while the origin of the remaining widening (large distribution of stress or Raman inactive additional defects) is discussed.
Owing to its unique properties such as chemical stability, large potential windows of water stability (up to 3 V) and mechanical resistance, boron-doped diamond (BDD) thin films have been widely used as electrodes for electro-analysis and electrolysis.In this work we have studied surface structural modifications in BDD thin films grown by hot filament chemical vapor deposition (HFCVD) due to usage as anodic working electrode in H3PO4 aqueous solution (pH=1, 2) up to 1000 h. With the powerful tool of Micro-Raman spectroscopy we show nonuniform structural variations of the diamond lattice. Modifications in the electrochemical properties has been observed while BDD electrodes were used as anodes. Moreover, by modelling the Fano interaction between discrete phonon states and the degenerate continuum of states, we point out an increase of the acceptor levels as a function of the electrode working hours.These experimental evidences indicate an anomalous behaviour of hydrogen loaded in the films during the growth process. A model based on the hydrogen–boron interaction could explain the observed modifications in Fano coupling.
Glassy carbon is a technologically important material widely used in products such as electrodes and high-temperature crucibles. However, the properties which make glassy carbon so valuable in these applications are poorly understood, since its detailed atomic structure is not known. A model for the structure of glassy carbon put forward many years ago has gained wide acceptance, but appears to suffer from serious shortcomings. In particular, it fails to account for the chemical inertness of the carbon, and for its high proportion of closed porosity. Here I show, using high-resolution transmission electron microscopy, that glassy carbons obtained from commercial suppliers contain a high proportion of fullerene-related structures. On the basis of these observations, models are put forward for the structures of 'low-temperature' and 'high-temperature' glassy carbons which incorporate non-six-membered rings.
This paper reports on the influence of the surface termination H-, HO-, NH2- of boron-doped diamond BDD electrodes on the oxygen reduction reaction ORR in alkaline solution. The aminated BDD surface displays a higher oxygen reduction current density and a positive shift in the oxygen reduction potential compared to H- and HO-terminated BDD surfaces. The behavior is
most likely due to a preferential adsorption of oxygen species on the NH2 termination. The ORR mechanism on the H-, HO-, and NH2-terminated BDD surfaces was investigated for the first time using electrochemiluminescence ECL of luminol. The results indicate that the ORR proceeds via a two-electron process on H-terminated diamond, while a four-electron pathway is observed for
oxidized and aminated BDD electrodes. We further show that the ECL approach can be easily extended to investigate the ORR mechanism on different electrodes and composite materials. The influence on the surface termination on the reduction of oxygen on gold-nanoparticle-modified BDD electrodes has been studied.
The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
Boron-doped diamond electrodes prepared by chemical vapor deposition were used to determine if phenol could be oxidized to
Cyclic voltammetry showed that phenol was oxidized by the diamond electrodes and remained electroactive after multiple cycles.
Experiments were also run with a flow cell in which 1 L of 10 mM phenol in 0.1 M
was circulated through the cell and the total organic carbon (TOC) was monitored as a function of time and cell current.
The TOC in solution was reduced from ∼1% to <0.1% with no observable decrease in decomposition rate. This means that the reacted
phenol was converted completely to
© 2001 The Electrochemical Society. All rights reserved.
The electrochemical degradation of p-nitrophenol (PNP) at boron-doped diamond (BDD) and platinum (Pt) anodes was studied by varying the parameters such as Cl(-) concentration, pH of aqueous medium and applied current density. The results obtained were explained in terms of in situ concomitant generation of hydroxyl radicals and chloride based oxidant species. The degradation of PNP was highly promoted in low concentration of NaCl electrolyte (less than 0.10M), on contrary, the mineralization efficiency was poor at both BDD and Pt anodes with the NaCl concentration up to 0.20M, which was ascribed to the formation of refractory chlorinated organic compounds. A maximum of 100% and 70% of COD removal was achieved in 5h of electrolysis period using both BDD and Pt anodes under similar experimental conditions. Kinetic study indicated that the degradation of PNP at BDD and Pt anodes followed pseudo-first-order reactions, and the reaction rate constant (k(s)) of the former was observed to be higher than that of the latter. Besides COD, conversion of PNP into various intermediate compounds and their degradations were also monitored. The mechanisms for PNP degradation at BDD and Pt anodes were proposed separately by considering the nature of respective intermediate species and their concentrations.
An electrochemical oxidation using a highly boron-doped diamond (BDD) electrode has been tested for the treatment of solutions containing ionic liquids (ILs). The double-sided Si/highly BDD electrodes were synthesized by microwave plasma enhanced chemical vapour deposition (MW PE CVD). Investigation of the electrode surface with scanning electron microscopy (SEM) confirmed that the synthesized layers were continuous and formed densely packed grain structure. The structure of BDD was confirmed by Raman spectra analysis. The effect of IL structure as the kind of electrolyte (Na2SO4 and NaCl) has been investigated. Electrolyses were conducted in an undivided electrolytic cell under galvanostatic conditions. The efficiency of the process has been evaluated in terms of variations of IL concentrations and chemical oxygen demand (COD) removal. Results show that pyridinium ILs were easier removed than imidazolium salts. The intermediates of electrochemical degradation of 1-butyl-3-methylimidazolium salt were detected, and IL degradation pathway was proposed based on the analytical results. It was suggested that •OH radicals produced by water electrolysis attacked IL to form its derivatives with keto groups substituted to imidazolium ring. These compounds underwent ring breakage, which led to the formation of aliphatic acids that were eventually mineralized by electrolysis to CO2. Other by-products were obtained by cutting one of the side chains substituted to N atoms in imidazolium ring. Additionally in NaCl electrolyte chloroorganic by-products were identified.
A method for improving the nucleation density of nanocrystalline diamond growth is demonstrated. Detonation nanodiamond powder was bead-milled and processed to stable aqueous colloid of core particles. This colloid was applied to various substrates to yield a very high density of individual spaced diamond nanoparticles. These diamond islands act as nucleation sites for chemical vapour deposition of nanocrystalline diamond.
In this paper an amperometric method that makes use of a the rotating ring-disc electrode (RRDE) configuration is described for the determination of the chemical oxygen demand (COD). It is shown that the strong oxidant necessary in COD measurements can be generated by an electrolytic in situ formation of an aggressive species, at the disc part of the ring-disc electrode, that oxidises the compounds that contribute to the COD. The excess of aggressive species formed reacts further to oxygen, which is determined at the ring electrode. Compensation of the disc current signal for the ring current signal finally results into the COD value of the solution. In this paper the COD value of real samples from a textile and a photo developing company were analysed and it was shown that a precision of 1% could be obtained within the range of 20–25,000 mg l−1. An important advantage is the fact that the COD value of a solution of unknown composition can be obtained within 1 min after calibration of the electrode system.
The early growth stages of chemical vapor deposition (CVD) diamond on a sol–gel TiO2 film with buried ultra dispersed diamond seeds (UDD) have been studied. In order to investigate the diamond growth mechanism and understand the role of the TiO2 layer in the growth process, high resolution transmission electron microscopy (HRTEM), energy-filtered TEM and electron energy loss spectroscopy (EELS) techniques were applied to cross sectional diamond film samples.We find evidence for the formation of TiC crystallites inside the TiO2 layer at different diamond growth stages. However, there is no evidence that diamond nucleation starts from these crystallites. Carbon diffusion into the TiO2 layer and the chemical bonding state of carbon (sp2/sp3) were both extensively investigated. We provide evidence that carbon diffuses through the TiO2 layer and that the diamond seeds partially convert to amorphous carbon during growth. This carbon diffusion and diamond to amorphous carbon conversion make the seed areas below the TiO2 layer grow and bend the TiO2 layer upwards to form the nucleation center of the diamond film. In some of the protuberances a core of diamond seed remains, covered by amorphous carbon. It is however unlikely that the remaining seeds are still active during the growth process.
A new application of boron-doped diamond (BDD) electrode was developed for detecting chemical oxygen demand (COD) by amperometric method. The effects of some basic experimental parameters including pH and applied potential on the response of the BDD electrode were investigated and the optimal operating conditions were obtained. In the COD tests of standard samples, a wide linear range of 20–9000 mg l−1 COD and a low detection limit of 7.5 mg l−1 COD were well established with the present approach. Additionally, the BDD sensor was successfully employed to determine the COD of real samples from various chemical or pharmaceutical wastewaters and the performance still kept stable after over 400 measurements. The results obtained indicated that, as compared with the conventional COD determination techniques, the proposed sensor was an environmentally friendly method with the advantages of short analysis period, simplicity, and no requirement of complicated sample pretreatment even for a sample containing relatively high concentration of organic pollutants.
The investigation of the film structure of diamond-like carbon films was the main objective of this work. Films within the structural systems of hydrogenated tetrahedral amorphous carbon (ta-C:H), silicon doped hydrogenated amorphous carbon (a-C:H:Si) and nitrogen doped amorphous carbon (a-C:N) were deposited at substrate temperatures of well below 100 °C. As deposition methods ion beam deposition, reactive unbalanced magnetron sputtering of silicon as well as infrared pulsed laser deposition (IR-PLD; λ=1064 nm) were studied. By the use of Raman spectroscopy it was found, that for high kinetic ion energy film deposition processes, i.e. ion beam deposition, the structure and properties of the ta-C:H films can be controlled by the kinetic energy of carbon species involved during film growth. For deposition techniques being typically known for low ion energies like magnetron sputtering or IR-PLD, applied for deposition of a-C:H:Si and a-C:N films, process tuning involves the study of the effects of inert gas/ reactive gas flow and the type of the reactive gas.
In this paper the electrochemical degradation of chlorobenzene (CB) was investigated on boron-doped diamond (BDD) and platinum (Pt) anodes, and the degradation kinetics on these two electrodes was compared. Compared with the total mineralization with a total organic carbon (TOC) removal of 85.2% in 6 h on Pt electrode, the TOC removal reached 94.3% on BDD electrode under the same operate condition. Accordingly, the mineralization current efficiency (MCE) during the mineralization on BDD electrode was higher than that on the Pt electrode. Besides TOC, the conversion of CB, the productions and decay of intermediates were also monitored. Kinetic study indicated that the decay of CB on BDD and Pt electrodes were both pseudo-first-order reactions, and the reaction rate constant (ks) on BDD electrode was higher than that on Pt electrode. The different reaction mechanisms on the two electrodes were investigated by the variation of intermediates concentrations. Two different reaction pathways for the degradation of CB on BDD electrode and Pt electrode involving all these intermediates were proposed.
The DiaCell® technology has been successfully tested against Legionella infection in several water types and under various working conditions. Depending on the water composition, Legionella can be completely inactivated with current densities as small as 50 mA/cm2 with low contact times (<5 min). The higher the oxidant concentration in the electrolyzed water, the more rapid is the Legionella inactivation after injection. Bicarbonates in contaminated water were identified as very good supports for electrochemical disinfectants production for Legionella inactivation without high chlorine concentration. At the same time, sulfates in water do not provide any disinfection capacity by DiaCell® electrolysis.
Most approaches to electron conduction from electrode to the enzyme requires the use of mediators – molecular relays which can take electrons from the electrode and deliver them to the redox sites of the enzyme. In the present paper, the biocatalytic reduction of oxygen to water in the presence of laccase is shown to proceed on the boron-doped diamond at highly positive potentials and without any additional mediator. The onset of catalytic reduction current appears at 0.805 V vs. NHE in solutions of pH 5.2. Laccase is either dissolved in the solution or trapped on the BDD electrode in a thin film of lipidic cubic phase. The remarkable stability of the modified electrode, avoiding the use of mediators and positive potential of the dioxygen reduction process make the BDD–laccase system especially interesting for applications in electrochemical sensing and microbiofuel cells.
As the boron incorporation level and the wavelength of the exciting laser were varied, we observed systematic modifications of the Raman spectra of homoepitaxial diamond films. A pronounced change in the lineshape of the zone-center optical Raman peak as well as a wide and structured signal at lower wavenumbers appeared simultaneously when the boron incorporation was increased above an abrupt threshold around 3×1020 cm−1. This threshold was found to depend on the excitation laser wavelength. Possible origins for the wide peaks at 500 and 1225 cm−1 are also discussed.
A photocatalytic sensor for the determination of chemical oxygen demand (COD) with flow injection analysis (FIA) based on the photocatalysis of organic compounds in the presence of titanium dioxide (TiO2) beads in a photochemical column is described. The sensor was developed in conjunction with TiO2 beads in the photochemical column and with an oxygen electrode as the sensing part. The sensor signal was observed as a result of the detection of dissolved oxygen changes due to photocatalytic oxidation of organic compounds in the sample solution. This sensor responded linearly to the CODMn of artificially treated wastewater (AWW) in the range of 0.12–8 ppm. A complete analysis, including sampling and washing, took about 10 min. The sensor was stable for over 15 days and has successfully been applied to the determination of COD in lake samples.
The electrochemical oxidation of four aromatic amines, with different substituent groups, 3-amino-4-hydroxy-5-nitrobenzenesulfonic acid (A1), 5-amino-2-methoxybenzenesulfonic acid (A2), 2,4-dihydroxyaniline hydrochloride (A3) and benzene-1,4-diamine (A4), was performed using as anode a boron-doped diamond electrode, commercially available at Adamant Technologies. Tests were run at room temperature with model solutions of the different amines, with concentrations of 200 ppm, using as electrolyte 0.035 M Na(2)SO(4) aqueous solutions, in a batch cell with recirculation, at different current densities (200 and 300 A m(-2)). The following analyses were performed with the samples collected during the assays: UV-Vis spectrophotometry, chemical oxygen demand (COD), total organic carbon (TOC), total Kjeldahl nitrogen, ammonia nitrogen, nitrates and HPLC. Results have shown a good electrodegradation of all the amines tested, with COD removals, after 6 h assays, higher than 90% and TOC removals between 60 and 80%. Combustion efficiency (η(C)), which measures the tendency to convert organic carbon to CO(2), was also determined for all the amines, being η(CA1)<η(CA2)<η(CA3)<η(CA4)=0.99.
Boron-doped diamond electrodes, both as-grown and polarized anodically under different conditions, were prepd. in order to study the chem. and electrochem. changes of diamond and clarify the role played by the surface-state d. Many different treatments were employed: as-grown (BDDag), mildly polarized (BDDmild), strongly polarized in perchloric acid (BDDsevere), and strongly polarized in a sulfuric acid-acetic acid mixt. (BDDAcOH). Charge transfer processes at the electrode surface were studied by cyclic voltammetry. Simple electron transfer processes such as the outer-sphere redox system ferri/ferrocyanide (FeIII/II;(CN)6) and complex charge transfer reactions such as the inner-sphere 1,4-benzoquinone/hydroquinone (Q/H2Q) redox reaction were chosen to test the electrochem. properties of the electrodes. The properties of the diamond electrodes were found to undergo strong modification as a function of surface treatment. The active surface area and the reaction rate consts. decreased significantly upon anodic polarization. Important drops in the charge carrier concn. on the surface and in true surface area led to hindrance of electron transfer at the electrode. [on SciFinder (R)]
A simple, environmentally friendly and continuous flow method was developed for the determination of COD based on a flow injection analysis (FIA) system, in which a BDD electrode was employed as the detecting element. The structure and the electrochemical behavior of BDD were investigated by a scanning electron microscope, Raman spectroscopy, and cyclic voltammetry, respectively. The results demonstrated thatthe high-quality BDD film prepared here was suitable to be used as an electrode, with which the COD measurement could be conducted. The effect of several important experimental parameters, such as applied potentials, pH, flow rates, and supporting electrolyte concentrations, on the analytical performance was investigated. Under optimized testing conditions, the proposed method was successfully applied in the COD analysis of synthetic samples. The linear range and the detection limit were 2-175 and 1 mg L(-1), respectively. In addition, the COD values determined by the proposed method compared well with those analyzed bythe conventional method as demonstrated by small relative errors.
Catalase was investigated as a possible catalyst of the electrochemical reduction of oxygen on glassy carbon electrodes. The presence of catalase dissolved in solution only provoked a moderate current increase, which was fully explained by the catalase-catalysed disproportionation of hydrogen peroxide (Scheme I). When catalase was adsorbed from dimethylsulfoxide on the surface of electrodes that did not undergo any electrochemical pre-treatment (EP), catalase efficiently catalysed oxygen reduction via direct electron transfer from the electrode (Scheme II). The results are discussed with respect to the electrode surface properties and the enzyme structure.
A chemically modified electrode based on the carbon nanotube film-coated glassy carbon electrode (GCE) is described for the simultaneous determination of dopamine (DA) and serotonin (5-HT). The multiwall carbon nanotube (MWNT) film-coated GCE exhibits a marked enhancement effect on the current response of DA and 5-HT and lowers oxidation overpotentials. The responses of DA and 5-HT merge into a large peak at a bare GCE, but they yield two well-defined oxidation peaks at the MWNT film-coated GCE. The experimental parameters were optimized, and a direct electrochemical method for the simultaneous determination of DA and 5-HT was proposed. The interference of ascorbic acid (AA) was investigated, and the results showed that a large excess of AA did not interfere with the voltammetric responses of DA and 5-HT. The modified electrode has been successfully applied for the assay of 5-HT and DA in human blood serum.
The anodic behavior and determination of pefloxacin on boron-doped diamond and glassy carbon electrodes were investigated using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. In cyclic voltammetry, pefloxacin shows one main irreversible oxidation peak and additional one irreversible ill-defined wave depending on pH values for both electrodes. The results indicate that the process of pefloxacin is irreversible and diffusion controlled on boron-doped diamond electrode and irreversible but adsorption controlled on glassy carbon electrode. The peak current is found to be linear over the range of concentration 2x10(-6) to 2x10(-4)M in 0.5M H(2)SO(4) at about +1.20V (versus Ag/AgCl) for differential pulse and square wave voltammetric technique using boron-doped diamond electrode. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. Selectivity, precision and accuracy of the developed methods were also checked by recovery studies. The procedures were successfully applied to the determination of the drug in pharmaceutical dosage forms and humans serum samples with good recovery results. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and biological samples, respectively.
- M A J Rodgers
- E L Powers
M.A.J. Rodgers, E.L. Powers, Oxygen and Oxyradicals in Chemistry and Biology,
Academic Press Inc, New York, 1981.