Chemical Thermal Oxidation Research Articles

Fire history of the western Amazon basin recorded by multiple pyrogenic carbon proxies

Charcoal abundance has been used as a fire proxy to reconstruct human settlement and climate records, but analyses of pyrogenic carbon (PyC) have become more widespread. To compare these proxies, fire records spanning the past 3000 y of Western Amazon Lakes Ayauchi, Gentry and Parker region soil and sediments were determined by visually identified charcoal, chemical-thermal oxidation (CTO) and benzene polycarboxylic acid (BPCA) markers. Charcoal represented the smallest portion of PyC and, with its irregular distribution, it likely indicated only local or large fires. PyC via CTO concentrations were highest and most uniform, suggesting lower sensitivity in detecting fire. BPCA-derived PyC distributions in soils were consistent with more human occupation and higher temperature fires in the Lake Ayauchi region and, in lake sediments, BPCA-derived PyC bore the closest resemblance to patterns of climate and human influence. Thus, BPCAs were more sensitive indicators of fire over regional scales. The combined information from multiple fire proxies revealed a history of frequent fires in western Amazon. Lake Ayauchi region had greater fire frequency and higher temperature fires than the Gentry/Parker region, suggesting greater human occupation. The greater fire frequency in wetter periods and regions of western Amazon, suggest a major influence of human activity on PyC production over the past 3000 years. Each fire proxy examined in this study had strengths and weaknesses and the use of a combination of fire proxies can provide a fuller picture of fire history than any single approach.

A response surface methodology optimization for efficient photocatalytic degradation over reusable CuxO/TiO2 nanocomposite on copper wire

In this study, the CuxO/TiO2 (x=1,2) nanocomposite photocatalyst was prepared via chemical-thermal oxidation followed by the sol-gel method on the copper wire. The characterization analysis indicated the co-existence of two types of copper oxides along with TiO2 and proved the formation of multicomponent heterostructure between semiconductors. A mixture of nanowires nanoparticles morphology was observed for the sample. The estimated band gap energy of the nanocomposite was 1.85 eV, which can be suitable for photocatalytic activity under visible light irradiation. A three-level three-factor Box-Behnken design (BBD) based on the response surface methodology (RSM) approach was used to determine the effects of parameters including pH, initial dye concentration, and photocatalyst dosage on the photocatalytic degradation of methylene blue (MB) dye. The significance of the factors was confirmed by employing the analysis of variance (ANOVA) with a 95% of confidence level. The interaction effect evaluation revealed that the pH and dye concentration are the most important process variables. The optimal values of the operating factors, including a pH of 11, dye concentration of 2.5 mg L−1, and photocatalyst dosage of 0.011 g mL−1, were specified to achieve a superior dye degradation efficiency of around 99%. It has been demonstrated by the reusability experiments that its wire form allows it to have high stability and ease of recovery. The kinetics study demonstrated the well fitted of the Langmuir-Hinshelwood (L-H) model to the dye photodegradation by the nanocomposite.

Surface modification of Cu2O-CuO photocatalyst on Cu wire through decorating with TiO2 nanoparticles for enhanced visible light photocatalytic activity

In this paper, the fabrication of Cu2O-CuO/TiO2 nanocomposite photocatalysts on Cu wire was performed successfully via chemical-thermal oxidation and sol-gel process. The chemical-thermal oxidations were applied for Cu2O-CuO nanostructure fabrication on the Cu wire surface. The sol-gel process was utilized for TiO2 nanoparticles decoration as a surface modification process for photocatalytic activity improvement. The X-ray diffraction analysis (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed the coexistence of multiple components including Cu2O, CuO, Cu, and TiO2 in the nanocomposite. Field emission electron scanning microscopy (FESEM) results demonstrated remarkable changes in morphology by applying different preparation conditions. The calculated band gap energies from UV–vis diffuse reflectance spectra (DRS) were in the range of 1.72–1.96 eV demonstrating their activity under visible light illumination. Photoluminescence (PL) data indicated delayed recombination of electrons - holes with surface modification due to the formation of heterostructure in the nanocomposite. The investigation of the photocatalytic performance was performed by methylene blue (MB) and methylene orange (MO) dye degradation under visible light illumination and 87 % degradation efficiency was obtained after 120 min. The active species trapping tests involving scavengers demonstrated that the superoxide radicals and holes play more noticeable roles compared to hydroxyl radicals in photocatalytic degradation. The ability to easily separate photocatalyst wires from aqueous solution along with good stability after several cycles of use in degradation is a unique feature of the prepared photocatalysts.

CNTs-copper oxide nanocomposite photocatalyst with high visible light degradation efficiency

CuxO (x = 1 or 2)/Carbon nanotubes (CNTs) nanocomposite was prepared through a two-step process including copper electroless deposition on CNTs followed by chemical-thermal oxidation. The effect of electroless deposition time and hence copper oxide content on the photocatalytic activity was studied, and 30 min of deposition was optimal. X-ray diffraction (XRD) and Raman results confirm the formation of both crystalline CuO and Cu2O phases. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed the dispersion of copper oxide nanoparticles onto the surface of CNTs. The diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) results showed that decreasing the copper oxide content decreases the bandgap and the electron-hole pairs recombination rate. The photocatalytic activity was investigated for the degradation of methyl orange (MO) and methylene blue (MB) under visible light irradiation. Relatively complete methylene blue (MB) degradation was obtained after 120 min for a 2 mg/L solution, while about 70% of methyl orange (MO) was degraded. The stability of the sample was also investigated, and the sample was able to maintain its performance after three cycles.

Titania-decorated copper oxide nanophotocatalyst powder: A stable and promoted photocatalytic active system

In this work, the synthesis of the CuO-Cu2O nanocomposites decorated with TiO2 nanoparticles was performed by chemical-thermal oxidation and subsequently by the sol–gel method. The X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM) showed using different furnace atmospheres lead to the formation of nanocomposites with variable components content with a mixture of special morphology. The Energy Dispersive X-Ray Analysis (EDX) confirmed the existence of Ti, Cu, and O elements in the composite material. The X-ray photoelectron spectroscopy (XPS) data suggest the presence of CuO and Cu2O species in addition to the TiO2 phase in the as-prepared composite samples. Transmission electron microscopy (TEM) and UV–vis spectroscopy indicated the successful fabrication of multiple heterostructures of TiO2 and copper oxides components. The assessment of gas-phase photocatalytic performance in the 2-propanol photodegradation under both UV and visible light irradiation was done through the measurement of the reaction rate and quantum efficiency. The composite photocatalysts demonstrated about 2.5 times more active photocatalytic behavior in gas phase photo-oxidation compared with the pure CuO-Cu2O and titania because of the simultaneous presence of different copper oxide types in the structure and TiO2 nanoparticles as a surface decorated part. A cascade-type mechanism was also proposed for the photocatalytic behavior of the system. Furthermore, the stability of the specimens was proved during the photocatalytic reaction.

Photodegradation of dyes in batch and continuous reactors by Cu2O-CuO nano-photocatalyst on Cu foils prepared by chemical-thermal oxidation

In this study, CuO-Cu2O nanocomposite photocatalyst on Cu foils was synthesized by chemical-thermal oxidation. In the chemical step Cu(OH)2 forms and in the thermal step, it turns to CuO and Cu2O. The X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM) showed the synthesized Cu/CuO-Cu2O nanocomposite contains nanorods distributing on the polyhedral copper oxide matrix. One-step thermal oxidation of Cu(OH)2 at 500 °C under nitrogen atmosphere has a denser distribution of the nanorods on the truncated octahedral matrix. Transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS) showed the formation of a heterostructure of CuO nanorods on the Cu2O matrix with the band gap energy of 1.35 eV. Photoluminescence spectroscopy (PL) indicated higher electron-hole separation efficiency in the presence of more nanorods. The photocatalytic activity was investigated by Methylene blue (MB) and Methyl orange (MO) degradation in two new batch and continuous reactors with and without air bubble flow under visible light irradiation. The continuous reactor not only was closer to the real application but also has faster kinetics and higher water purification capacity. The degradation in this reactor for 300 mL of 2 mg L−1 MB solution was 55 % within 5 h with 0.8 cm2 mL−1 of photocatalyst. X-ray photoelectron spectroscopy (XPS) revealed the increase in the CuO/Cu2O ratio and the adsorbed oxygen on the surface after the degradation process. Different colors of light-emitting diodes (LED) were used as an illumination source. The maximum photonic efficiency was obtained for the blue color.

Electrochemical and Mechanical Effects of Acid and Thermal Treatments of Carbon Fiber

This paper presents modification method toward preparing activated structural carbon fibers (CFs) possessing both good electrochemical and mechanical properties. The surface treatment of CFs has been carried out by chemical and chemical–thermal oxidation, and supercapacitors have been fabricated with CF electrodes. Effects of surface treatment on fiber surface characteristics, mechanical properties, and electrochemical performances were investigated. Results show that proper treatment of CF by chemical–thermal oxidation provides an effective way to enlarge the fiber surface area (increase around 45‐fold), strengthen fiber surface chemical activity, and fiber tensile strength (increase around 20%) as well as its energy storing ability (increase around 129‐fold).

Contribution of black carbon in recent sediments of the Gulf of Cadiz: Applicability of different quantification methodologies

In the Southwestern Iberian Peninsula, vegetation fires are rather common, and produce a considerable amount of charred material that, due to erosion, is fluvially transported to the continental margins. The present study constitutes the first comparative assessment of the contribution of this charred material (generally black carbon, BC) to marine sediments of the inner continental shelf of the Gulf of Cádiz (GoC). Given the ambiguity of BC definition and the heterogeneity of quantification techniques, four of the most common and well established methodologies were applied to obtain a representative range of the BC content on four surface sediments: chemical-thermal oxidation (GBC), molecular markers (benzenopolycarboxylic acids, BPCA), thermogravimetry coupled to mass spectrometry (TG-DSC-QMS), and chemical oxidation with sodium chlorite. The BC results obtained for the GoC sediments are compared, and the applicability of each technique on marine sediments is discussed. The mean BC values of the four methods (4.4–14.4% total organic carbon) were within ranges previously reported for marine sediments from diverse origins. However, a large variability was observed within individual samples when comparing the BC results obtained with the four methods (relative standard deviation from 31% to 75%). The BPCA approach produced the highest BC values, whereas the GBC method the lowest. This reflects the analytical variability derived from the different windows composing the BC continuum. The results derived from the TG-DSC-QMS application generated certain uncertainties, despite the correction factor introduced to reduce the BC overestimation previously reported for this method. Considerable differences in the BC content of spatially close samples evidenced the complexity of coastal currents and sediment fluxes in the area, suggesting the existence of other factors affecting the BC distribution. The lack of correlation between the BC and TOC, as well as between the BC and lignin contents in all samples, ruled out the occurrence of charring artifacts. Preferential degradation and/or erosion of BC could explain the BC distribution in the area. The use of ancillary terrigenous biomarkers (lignin and inorganic silica) pointed to a preferential fluvial transport of the terrestrial organic matter and indicated that the longer distance from the source, the greater degradation of the OM. In addition, the northern dominant winds in the region may have favored the additional introduction of airborne transported BC in the marine system.