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This work proposed new black-wattle tannin/kraft lignin H

This work aimed to evidence the potential use of tannin-based carbon xerogel as a co-catalyst in photocatalytic processes based on solar light. Specifically, the tin (IV) oxide/carbon xerogel photo...

RESUMO Explorou-se a influência de diferentes precursores carbonosos no desenvolvimento de fotocatalisadores g-C3N4/xerogel de carbono/ZnO. O acoplamento entre o óxido de zinco e o nitreto de carbono grafítico é adequado para impulsionar a degradação de poluentes orgânicos. A função do xerogel de carbono é melhorar a transferência de cargas e aumentar a atividade do catalisador sob radiação solar. Foram usados diferentes taninos comerciais (PHENOTAN AP, AG e BS) para avaliar o efeito do precursor carbonoso nas propriedades do compósito. O óxido de zinco possui estrutura cristalina hexagonal. A espectroscopia de reflectância difusa mostrou que os materiais absorvem radiação na região do espectro visível, sendo o material preparado com PHENOTAN AP o que apresentou maior capacidade de absorção. A análise de microscopia eletrônica de varredura mostrou que os materiais são compostos por aglomerados de partículas que tendem a esfericidade. A análise de espectroscopia de energia dispersiva, feita apenas para o material PHENOTAN AP, mostrou que os elementos que compõe o material estão homogeneamente distribuídos na matriz. Por meio da isoterma de nitrogênio, observou-se que os materiais possuem isoterma do tipo IV-H3, sendo que o material PHENOTAN AP apresentou a maior área superficial. A análise de distribuição de poros mostrou que o diâmetro de maior ocorrência se encontra entre 20 e 40 nm. Por meio da termogravimetria, observou-se o material sintetizado com PHENOTAN AP apresenta maior estabilidade térmica. Foi observado que o precursor utilizado na síntese dos compósitos influencia significativamente a atividade fotocatalítica dos materiais. O compósito que apresentou a maior eficiência na fotodegradação do 4-clorofenol sob radiação solar foi o preparado com PHENOTAN AP devido à sua capacidade de absorção de radiação superior, maior área superficial e maior volume de poros. Não houve adsorção significativa do 4-clorefenol nos materiais produzidos, assim como não foi verificada lixiviação dos fotocatalisadores ternários durante o processo.

Considering the ever-increasing need for efficient wastewater treatment, this study focused on the development of new kraft lignin-based carbon xerogel/zinc oxide (XCL/ZnO w) photocatalysts. The inclusion of the carbon xerogel is expected to cause an improvement in charge transfer throughout the photoactivation process, consequently enhancing its overall photocatalytic efficiency. Characterization shows that the materials developed are composed of both zinc oxide and carbon xerogel. The addition of the lignin-based carbon xerogel caused a significant morphological modification to the composite materials, resulting in a greater specific surface area. Regarding the photocatalytic efficiency, the optimized composite (XCL/ZnO 1.0) displayed superior efficiency to the pure zinc oxide, especially when calcined at 700 °C, with an increase of 20% in the overall photodegradation capacity for the 4-chlorophenol (4CP) molecule. The XCL/ZnO 1.0 also displayed better performance than its tannin counterpart, previously reported in the literature, obtaining a 60% increase in the apparent reaction rate constant. The XCL/ZnO 1.0 also displayed better performance for the simultaneous hexavalent chrome (Cr (VI)) reduction/4CP oxidation reaction. Salinity and system pH had a significant influence on the efficiency of the 4CP photodegradation, as higher values of salinity and lower pHs caused a decrease in the overall efficiency of the process. At last, chronoamperometry and open-circuit potential tests confirmed the superiority of the XCL/ZnO 1.0 over the pure ZnO, highlighting the beneficial impact of the carbon xerogel on the charge transport dynamics of the composite.

This paper reports the development of new ZnO/carbon xerogel composites (XZn w) for photocatalytic applications. The use of black wattle tannin as a precursor to the carbon xerogel aimed at reducing costs and environmental impacts. The composites were characterized by diffuse reflectance spectroscopy (DRS), BET surface area, scanning electron microscopy (FEG-SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray diffraction (XRD). The photocatalytic performance of the materials was evaluated in the decomposition process of methylene blue, a known toxic pollutant. The impacts of the catalyst dosage and calcination temperature on the photocatalytic process were also examined systematically. The X-ray profiles of the XZn w evidenced the existence of the hexagonal structure of the zinc oxide (wurtzite) in the composites. The XPS and XRD analyses confirmed the incorporation of carbon in the zinc oxide crystalline structure. The higher carbon content resulted in a larger surface area. All composites presented the ability to absorb radiation in less energetic wavelengths, contrary to pure zinc oxide that only absorbs radiation of wavelengths below 420 nm. The optimal dosage and calcination temperature were found to be 0.2 g L−1 and 300 °C. All the developed composites displayed significant photocatalytic activities in the decomposition of methylene blue under both visible and solar light. The composites had superior photocatalytic efficiency under visible light when compared to pure zinc oxide. The XZn 0.5 presented the best degradation efficiency under visible radiation. All materials presented similar photocatalytic responses under solar light, evidencing the synergy between the carbon xerogel and the zinc oxide. The photocatalytic mechanism was evaluated by trapping experiments to be mainly controlled by the electron vacancies that are generated during the photoexcitation of the composites.

RESUMO O desenvolvimento de novos compósitos oxalato de zinco (ZnC2O4)/xerogel de carbono para aplicações fotocatalíticas foi avaliado. O uso do xerogel de carbono é justificado por sua alta condutividade, que facilita a separação de cargas geradas na estrutura do oxalato de zinco. A eficiência fotocatalítica dos materiais foi avaliada pela decomposição do azul de metileno. Os materiais foram produzidos pela dispersão do oxalato de zinco em gel de carbono, durante sua policondensação em meio ácido. Os difratogramas de raios-X evidenciam a existência da fase ?-ZnC2O4 no compósito desenvolvido. O material apresenta significativa absorção de radiação na faixa de comprimentos de onda visível. O compósito apresentou degradação completa do azul de metileno (10 mg L-1, 0.5 L) no sistema após 3 h sob luz solar simulada, com dosagem de 50 mg L-1 de catalisador, evidenciando o potencial uso desse material em processos de tratamento de efluentes. ABSTRACT The development of new ZnC2O4/carbon xerogel composites for photocatalytic applications has been evaluated. The use of carbon xerogel is justified by its high conductivity, which facilitates the separation of charges generated in the structure of zinc oxalate. The photocatalytic efficiency of the materials was evaluated by the decomposition of methylene blue. The materials were produced by dispersing zinc oxalate in carbon gel during its polycondensation in acidic medium. X-ray diffractograms show the existence of the ?-ZnC2O4 phase in the developed composite. The material has significant radiation absorption in the visible wavelength range. The composite showed complete degradation of methylene blue (10 mg L-1, 0.5 L) in the system after 3 h under simulated sunlight, with 50 mg L-1 catalyst dosage, showing the potential use of this material in treatment processes. of effluents.

This study is focused on the evaluation of the Rhodamine B photodegradation using ZnO/carbon xerogel composite as a photocatalyst, in order to enhance the photocatalytic process efficiency under visible light. The proposed synthesis employs tannin as a precursor for the carbon xerogel, which enhances the economic and environmental aspect of the composite. The synthesized materials have the hexagonal structure of the zinc oxide (wurtzite), which is homogeneously distributed on the carbonaceous matrix. The diffuse reflectance test shows that light absorption was significantly enhanced for the composite. The solar light-driven photodegradation results revealed that the synthesized composite achieved virtually complete degradation of the dye present in the solution in less than 3 h, in all concentrations tested. The results of visible light driven photocatalysis showed that the carbonaceous material presents better photoactivity than the pure oxide (70% and 40% degradation of Rhodamine B, respectively), due to the synergistic effect between the carbon xerogel and zinc oxide on the properties of the composite. The photocatalytic mechanism main active species are the photogenerated vacancies and superoxide radicals.

The present study investigates the modification of carbon black with ruthenium and niobium oxides and the application of the modified carbon material for the electrogeneration of hydrogen peroxide via oxygen reduction reaction. The modified carbon materials were characterized electrochemically using the porous microlayer technique on rotating ring-disc electrode. The modification of amorphous carbon black with 5.0% Ru05Nb95O (5.0% Ru05Nb95O/C) contributed to the enhancement of selectivity toward H2O2 electrogeneration, with current efficiency of 84.6% and a shift in potential of − 0.300 V. The most efficient material (5.0% Ru05Nb95O/C) was characterized by X-ray absorption spectroscopy, X-ray fluorescence and scanning electron microscopy. The application of gas diffusion electrodes for H2O2 generation in acid medium yielded 281.6 mg L−1 of H2O2 in 120 min of experiment at current density of 100 mA cm−2. The concentration of H2O2 electrogenerated on the modified carbon material was 33.6% higher compared to the concentration electrogenerated on the unmodified carbon material (210.8 mg L−1) under the same experimental conditions.

This paper evaluates the influence of synthesis route (acidic or alkaline) on the structure, morphology, and photocatalytic properties of ZnO/Carbon xerogel composites. Structurally, both classes of materials present the wurtzite phase of zinc oxide. Composites derived from acidic route displayed facile thermal degradation of the zinc oxalate precursor when compared with pure zinc oxalate. Morphology-wise, materials produced through alkaline route are composed of nodular and plate-like particles, whereas acidic route composites are heterogeneously formed by large polyhedral particles and small particle agglomerates. Elemental distribution analysis confirms the heterogeneity of the acidic route composites, showing clear phase separation between the ZnO and the carbon xerogel. The composites prepared using the alkaline route are superior in the photodegradation of 4-chlorophenol, probably due to higher homogeneity and synergy between the semiconductor and carbonaceous phases. The superiority of alkaline route composites is confirmed by electrochemical impedance spectroscopy, which shows that such materials have enhanced charge separation capability.

The effect of synthesis medium (ethanol and water) on ZnO/Carbon xerogel photocatalysts was studied in order to increase the efficiency of the photocatalytic degradation of 4-chlorophenol and bisphenol A. The use of carbon xerogel is justified due to its excellent electrical conductivity, high surface area and porosity. The effect of the carbon content in the composites was also evaluated. The composites were characterized using scanning electron microscopy, transmission electron microscopy, dispersive energy spectrometry, X-ray diffractometry, infrared spectroscopy, nitrogen isotherms, differential scanning calorimetry, thermogravimetry, electrochemical impedance spectroscopy and Raman spectroscopy. All materials present the hexagonal crystalline structure of zinc oxide. Materials without carbon in their composition also presented the zinc hydroxychloride monohydrate phase. X-ray diffractograms and bandgap values obtained confirm the incorporation of carbon in the crystalline structure of zinc oxide. Materials produced in ethanol medium have lower values of crystallite and particle size, as well as higher graphite contents in their composition and higher specific surface area. All materials displayed photocatalytic activity when subjected to visible and solar radiation. Materials produced in ethanol displayed superior performance when compared to those synthesized in aqueous medium. The maximum values found for the degradation of 4-chlorophenol and bisphenol A were 88% and 78%, respectively, after 5 h. The mechanism of photocatalysis is strongly influenced by the generation of hydroxyl radicals and the materials were stable for three cycles of reuse. The electrochemical impedance spectroscopy confirms that the charge separation efficiency was optimized in the presence of the carbon xerogel and when the composite was produced in ethanol medium.

This project studied the development of niobium oxide-doped zinc oxide photocatalysts, aiming to increase the photocatalytic efficiency of zinc oxide (ZnO). Characterization results prove the existence of zinc oxide and niobium oxide (Nb2O5) in the developed material. The addition of niobium oxide caused an increase in specific surface area and a decrease in the gap energy of the material. The results of 4-chlorophenol photodegradation show that the modified material displayed higher photocatalytic activity than pure ZnO. The superior photocatalytic activity is derived from the morphological and structural properties of the modified material, as well as from the heterojunctions formed between the semiconductors. The greater efficiency of charge transfer in the Nb2O5-doped material is demonstrated by the electrochemical impedance spectroscopy.

This work aimed to study the development and properties of Bi-doped ZnO/β-Bi2O3/Carbon xerogel composites towards visible light photocatalysis applications. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dispersive energy spectroscopy, infrared spectroscopy, nitrogen adsorption isotherms, Raman spectroscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the developed composites was evaluated through the photodegradation of the 4-chlorophenol molecule and by chronoamperometry tests. The results obtained show that the calcination temperature poses a major influence in the final structure of the materials developed. The calcination temperature of 600 °C resulted in the formation of the β-Bi2O3 and Bi0 phases, consequently enhancing the photocatalytic activity of the composites due to the increased charge mobility provided by the heterojunctions between zinc oxide, carbon xerogel, bismuth oxide and metallic bismuth. The composite with intermediate bismuth composition (XC/ZnO–Bi2O3 5%) displayed the best photocatalytic response among the materials tested, which was confirmed by its increased photocurrent generation capability. The photocatalytic mechanism is highly dependent in the generation of hydroxyl radicals and the composite presents good reusability properties.

Agradecimentos: The authors acknowledge the financial support provided by the São Paulo Research Foundation (FAPESP) (Grants Nº 2018/10492-1, Nº 2018/12035-7, Nº 2017/10118-0, Nº 2013/02762-5 and Nº 2018/16360-0) and by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Grants Nº 155550/2018-7 and Nº 405543/2016-6). The authors are also grateful to TANAC S.A., which supplied the black wattle tannin Abstract: This study examines the development of ternary photocatalysts based on titanium dioxide, niobium oxide, and carbon xerogel, aimed at increasing photocatalytic efficiency under solar light irradiation. The modifications proposed are focused on diminishing charge recombination and enhancing visible light sensitivity. The new photocatalyst was prepared using discarded titanium and niobium scraps and chips, whilst black wattle tannin was used as the carbon source. The X-ray diffractometry results show that the anatase form of titanium dioxide is present in the samples, whereas the niobium oxide presents itself in the amorphous structure. The incorporation of both carbon xerogel and niobium oxide into the TiO2 is confirmed by the infrared and energy dispersive spectroscopies. The diffuse reflectance results show that the materials containing carbon xerogel present a significantly higher visible light absorption, whilst the combined effect of the modifications proposed caused the gap energy of the ternary material to drop noticeably. The photocatalytic efficiency of the ternary material was superior to the ones found for the pure oxides and binary material, probably due to its lower value of bandgap and enhanced charge separation efficiency, as confirmed by the electrochemical impedance tests FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

This work evaluates the properties of a new Nb2O5-doped ZnO/carbon xerogel photocatalyst and its efficiency for the degradation of 4-chlorophenol under solar radiation. The development of this material is aimed at diminishing charge recombination during the photocatalytic process. The diffractograms obtained confirm the presence of the hexagonal zinc oxide structure in all samples, whereas the X-ray photoelectron spectroscopy confirms the presence of Nb2O5 on the structure of the ternary photocatalyst. The higher specific surface area of the Nb2O5-doped material, as well as the lower value of gap energy, can be ascribed to the presence of the newly incorporated metallic oxide into the structure of the materials, along with the carbon xerogel. The photocatalytic tests results show that the material with Nb2O5 in its composition exhibited superior efficiency in the degradation of 4-chlorophenol under simulated solar radiation, obtaining a much higher apparent reaction rate constant. Furthermore, the modification impacts the photocatalytic mechanism, which becomes greatly dependent on the hydroxyl radical.

This project studied the preparation of new Nb2O5/tannin-formaldehyde xerogel composites (XTF-wNb) for photocatalytical applications. The choice of tannin biomass and niobium recycled scraps as precursors is aimed at reducing costs and environmental impacts. The composites were characterized by diffuse reflectance spectroscopy (DR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray diffraction (XRD). The photocatalytic properties of the composites were evaluated by methylene blue decomposition. The influence of the catalyst dosage and the initial concentration of dye in the adsorption and photocatalysis processes were studied. The X-ray profiles of the XTF-wNb show the presence of niobic acid in the structure of the materials, proving the presence of the inorganic oxide in the matrix of these composites. The tannin/Nb ratio had a significant influence on the morphology of the formed composites, causing changes in the shape and size of the particles composing each material. All materials have pHPZC

This project aimed to evaluate the synthesis route influence in the structural, morphologic and photocatalytic properties of carbon xerogel/Nb2O5 composites. Infrared spectroscopy and X-ray diffractometry confirm the existence of niobium-based oxides in the composites, whereas the diffuse reflectance and energy dispersive spectroscopy prove the incorporation of the carbon xerogel. The XC-24Nb composite presented the best photocatalytical response, as it presented higher crystallinity, high surface area and superior carbon xerogel incorporation. The XC-24Nb carb was the least effective material, probably due to its considerably inferior surface area. The degradation of methylene blue is controlled by electrons and electron vacancies.

This study explores the development of metal doped hybrid Nb2O5/carbon xerogel photocatalysts. The materials were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, dispersive energy spectroscopy and X-ray diffraction. The X-ray diffractograms of the materials are characteristic of amorphous carbon. The palladium doped composite also exhibits the hexagonal phase of the niobium oxide. The chemical elements are evenly distributed on the materials, confirming the dispersion of the doping metals in the material matrix. All composite materials absorb radiation in the visible light region. All composites exhibited photocatalytic activity under visible radiation, except for the iron doped material. The palladium doped material showed superior efficiency in the degradation of methylene blue, due to its lower band gap and higher absorption of visible light.

This paper evaluates the feasibility of using niobium-based catalysts for the photodegradation of organic dyes. The metal oxides were prepared using niobium scraps and chips as precursors. The semiconductors were characterized by diffuse reflectance spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, infrared and Raman spectroscopy. The as-prepared anhydrous niobium oxide has a pseudohexagonal structure, whereas the hydrated niobium oxide is an amorphous material. The specific surface area of the hydrated niobium oxide is found to be double the area of its calcined counterpart. The photocatalytic efficiency of the materials was evaluated by methylene blue (MB) decomposition, measured by UV-visible spectroscopy. The effects of catalyst dosage and initial dye concentration were investigated in both the adsorption and photocatalysis processes. Increasing the initial MB concentration leads to increase the amount of adsorbed MB but to decrease the photocatalytic efficiency for all materials. In contrast, both the amount of adsorbed dye and the photocatalytic efficiency increase with increasing the catalyst dosage (0.5–2 g L−1). The highest photodegradation efficiency is achieved using UVC radiation. The specific surface area as well as the amount of acid sites, adsorbed water, and OH− surface groups on the catalyst surface demonstrates to be fundamental to the photocatalytic properties of the materials. Furthermore, the photocatalytic mechanism is controlled by superoxide and singlet oxygen species for the hydrated material, whereas the hydroxyl radical is the main active species in the photodegradation employing the anhydrous oxide. The hydrated material achieved a complete degradation of the methylene blue.

Activated carbon (ACAcai) was obtained from the activation of acai seeds at 800 °C under CO2 flow. The surface groups of the material were determined by Boehm titration and information about surface charge was obtained using the methodology of the point of zero charge (PZC). Boehm titration and PZC tests showed that the ACAcai sample has a basic character. The optimum pH range for the adsorption process is 3.5–8 and the optimum dosage is 0.1 g/50 mL of phenol solution. ACAcai has a surface area of 496 m2 g−1 and pore volume of 0.217 cm3 g−1. The adsorption kinetics follows the pseudo-second-order model. The Langmuir isotherm model satisfactorily described the experimental data. The maximum adsorption capacity obtained was of 133 mg g−1 at 25 °C. Deionized water, NaOH solution (0.1 M), and ethanol were used as desorption agents, but none of them showed promising results for the regeneration of ACAcai. The thermodynamic studies show that the adsorption process is exothermic, spontaneous, and favorable.

This work explored the synthesis and characterization of zirconium oxide/carbon xerogel composite, using the material as a photocatalyst in the photodegradation of methylene blue. The band gap energy of the samples was determined using diffuse reflectance spectroscopy. The crystallographic phase, morphology, elemental analysis, analysis of metal content and porosity of the samples was examined by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and infrared spectrometry, respectively. The methylene blue concentration was determined using a UV–vis spectrophotometer. The analysis results confirm the formation of zirconium oxide in its monoclinic crystal structure in the pure oxide. The composite presented amorphous structure. The zirconium oxide/carbon xerogel composite presented a higher radiation absorption, in all wavelengths tested. The results regarding the degradation of methylene blue confirm the existence of photocatalytic activity of the materials when submitted to the UVC wavelength. The XZrC composite presented considerably superior photocatalytic efficiency, when compared to the pure semiconductor, as the degradation obtained with the composite was 67% higher than the one obtained with the ZrO 2 .

The aim of this study was the development of low-cost tannin-formaldehyde xerogel/TiO2 (XTi-w) and carbon xerogel/TiO2 (XTiC-w) photocatalysts. The materials used as precursors were recycled titanium scraps and black wattle tannin extract, highlighting the low-cost approach employed in the synthesis. The materials were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, dispersive energy spectrophotometry, X-ray diffractometry, infrared and Raman spectroscopy. X-ray diffractometry showed that the XTiC-w have tetragonal crystalline structure (anatase), whereas the XTi-w has an amorphous structure. The Raman and infrared analysis also showed the presence of titanium dioxide in the composition of both XTi-w and XTiC-w. XTi-w and XTiC-w showed photocatalytic activity at the visible wavelength. Titanium dioxide displayed no photocatalytic activity at the visible wavelength. The XTi-60 composite displayed the highest efficiency in the removal of the methylene blue from the system, as well as good reusability properties. The radicals with higher influence in the photocatalytic reaction mechanism are the photo generated electron and the singlet oxygen molecule. The effect of the heat treatment is negative on the photocatalytic properties of the hybrids produced, due to the removal of acid sites, adsorbed water and OH surface groups.

This work explores the development of hybrid Nb2O5/carbon xerogel photocatalysts. The precursor materials used, such as tannin and recycled niobium scraps, enhance the economic and environmental aspects of the synthesis. The materials were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, dispersive energy spectroscopy, infrared spectroscopy, Raman spectroscopy and X-ray diffraction. The photocatalytic action of the material was evaluated by methylene blue decomposition as determined by UV–visible spectroscopy. Anhydrous niobium oxide has a hexagonal structure. The X-ray profiles of the materials developed (XC-wNb) are similar to Nb2O5, confirming the presence of inorganic oxide in the matrix of these composites. The chemical elements that compose the samples are homogeneously distributed on the surface of the samples, confirming the dispersion of the oxide in the carbonaceous matrix. The XC-wNb absorbs radiation in a considerably wider range than inorganic oxides, in this case, for the entire wavelength range used in the experiments, thereby suggesting the synergistic effect of xerogel and niobium oxide on the optical properties of the XC-wNb samples. All XC-wNb presented photocatalytic activity under visible radiation, evidencing the beneficial coupling effect on the photocatalytic properties of the material. The XC-24Nb was the most effective photocatalyst at the wavelength used due its composition, morphological and photochemical properties. The methylene blue photodegradation is controlled to a greater extent by reaction with the OH • radical. The XC-24Nb also presents high stability and reusability, which are optimal properties for industrial application.

This paper explored the development of a new zinc oxide/zinc sulfide/carbon xerogel composite photocatalyst aiming at the efficient 4-chlorophenol photodegradation under solar light. X-ray diffractometry highlights that the crystalline structure of zinc sulfide depended on the presence of zinc oxide, changing from face-centered cubic in the pure ZnS to hexagonal (2 H) in the composite. Furthermore, the addition of carbon xerogel to the composite led to a reduction in the particle size and an increase in the specific surface area. Photocatalytic results show that the ternary composite (XC/ZnO-ZnS) displayed the best photocatalytic response for 4-chlorophenol degradation among the tested materials. Such photocatalytic improvement is probably related to the formation of heterojunctions between the semiconductors and the carbonaceous phase, as well as the enhanced morphological properties of the composite. The superiority of the XC/ZnO-ZnS was further corroborated in the chronoamperometry tests, as it presented the highest photocurrent generation.

This paper reports the development of a new carbon xerogel/zinc oxide/tin oxide ternary photocatalyst and its application for the enhancement of photocatalytic response through the formation of heterojunctions composed of different phases. The results obtained from X-ray diffractometry showed that all the materials exhibited the hexagonal structure of zinc oxide. The application of infrared spectroscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses helped confirm the presence of tin oxide and carbon xerogel in the photocatalytic material developed in the study. All the materials evaluated in the study showed photocatalytic activity under both solar and visible radiations. Under visible light, the optimized ternary material displayed higher photoactivity for 4-chlorophenol degradation, with total degradation of 55% in 5 h. The results obtained from chronoamperometry tests showed that the ternary composite exhibited the highest photocurrent among the samples evaluated when the materials were subjected to solar radiation.

Agradecimentos: The authors acknowledge the financial support provided by the Sao Paulo Research Foundation (FAPESP) (Grants No 2018/10492-1, No 2018/12035-7, No 2017/10118-0, No 2013/02762-5 and No 2018/16360-0) and by the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) (Grants No 155550/2018-7 and No 405543/2016-6). The authors are also grateful to TANAC S.A., which supplied the black wattle tannin Abstract: This work aims to synthesize visible light-driven photocatalysts based on zinc oxide, polymeric graphitic carbon nitride (g-C3N4) and carbon xerogel. The addition of g-C3N4 and carbon xerogel to the zinc oxide is expected to hinder electron-vacancy recombination, increase specific surface area and reduce bandgap energy. The Raman spectroscopy and X-ray diffractometry confirm the presence of the wurtzite phase of zinc oxide in the materials. Furthermore, the X-ray diffractometry results show that C and N were likely incorporated into the structure of the zinc oxide in the ternary and binary materials, due to the distortion observed in the crystal lattice of the composites. The XPS analysis corroborates the presence of the g-C3N4 in the composite developed, as well as the incorporation of the carbon xerogel into the wurtzite structure. The addition of g-C3N4 and carbon xerogel resulted in significant changes on the morphology of the prepared materials, causing an increase in surface area and textural modification. The optimized ternary composite, which contains 0.25% of g-C3N4 (% w/w), has the highest photocatalytic response among all materials tested, obtaining 92% of 4-chlorophenol degradation under solar radiation and 72% under visible radiation, after 5 h. The enhanced photocatalytic activity of the ternary material can be linked to a superior charge mobility and higher visible light response, as shown by chronoamperometry tests and diffuse reflectance spectroscopy FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

This work aimed to study the effect of the spray drying technique on the morphological, structural, optical and photocatalytic properties of the Nb2O5/carbon xerogel composite. The results obtained show that the spray drying technique causes a significant change in the morphology of the composites, resulting in spherical and uniform particles. Structurally wise, the composite produced using spray drying has the hexagonal structure of the niobium oxide, whereas the material produced using evaporative drying has an amorphous structure. The optical properties of the composite were also affected, as the bandgap energy of the spray dried material is lower than the one obtained for the composite obtained through evaporative drying. The spray dried material presented superior adsorption capacity and photocatalytic efficiency, indicating that the modifications introduced by the spray drying are suitable to enhance the photocatalytic efficiency of the Nb2O5/carbon xerogel composite.

TFC was used for chromium ions (III and VI) adsorption from aqueous solution. The total chromium removal was strongly affected by pH changes and reached a maximum value at pH 1. The adsorption process was well described by the Langmuir model. The thermodynamic parameters exhibited the feasibility and the spontaneous nature of the adsorption. The optimum adsorbent dose obtained for chromium adsorption onto TFC was 0.1 g. The optimum contact time for chromium removal and treatment efficiency was 10 and 14 h, respectively. The kinetic studies showed that the adsorption process could fit into a pseudo-second-order model and the particle diffusion process was the rate-limiting step of the adsorption process. The desorbing agents studied did not show any promising result for the TFC regeneration process. The FT-IR results showed that the Cr(VI) removal onto TFC occurs through an indirect reduction mechanism. According to XPS spectrum, the majority of the adsorbed Cr is Cr(III), only a small quantity of Cr(VI) remains loaded on the TFC surface.

This work explores a new route for the synthesis of titanium dioxide using scraps and titanium chips, which are typically discarded as waste, as the precursor materials. The band-gap energy of the synthesised materials was determined using diffuse reflectance spectroscopy. The morphology, elemental analysis, crystallinity, and chemical structure of the synthesised materials were determined by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, and infrared and Raman spectroscopies, respectively. The X-ray and Raman analyses confirmed the formation of titanium dioxide in its tetragonal (anatase) crystalline form after heat treatment (400 °C, 2 h). Moreover, a mixture of (NH 4 ) 0,3 TiO 1,1 F 2,1 and anatase TiO 2 was obtained as a by-product. After heat treatment, this by-product was converted into fluorine-doped titanium dioxide, also in anatase crystalline form. The apparent crystallite size ( L c ) of anhydrous titanium dioxide was found to be smaller than that of the calcined by-product. The diffuse reflectance spectroscopy analysis revealed that the calcined by-product has a significantly higher absorption capacity at higher wavelengths, as well as a lower band-gap energy value. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analyses showed large particulates on which smaller particles are deposited and good dispersion of the elemental components. The anhydrous titanium dioxide sample presents a smaller particle size than the calcined by-product.

Tannin–formaldehyde cryogels (TFC) were synthesized by sol–gel polycondensation of low molecular weight and highly reactive modified tannin with formaldehyde using HCl as a catalyst. Carbon cryogels (CC) were obtained by the TFC pyrolysis at an inert atmosphere at 800 °C. Pyrolysis caused significant changes in the physical and chemical properties of the material. The pyrolysis induced the decomposition of acid superficial groups and the development of basic ones. Pyrolysis also provoked significant change in the pore volume, forming a great amount of micropores. TFC and CC showed amorphous and turbostratic structures, respectively. Unpurified samples had inorganic impurities in their compositions.

In this study, activated carbon based on the waste macadamia nut shells (MAC) was investigated for potential use as an adsorbent for phenol removal. The pseudo second-order kinetic model best described the adsorption process. The extent of the phenol adsorption was affected by the pH solution and the adsorbent dosage. Equilibrium data fitted well to the Langmuir model with a maximum adsorption capacity of 341 mg g−1. The calculated thermodynamic parameters suggested that the phenol adsorption onto MAC was physisorptive, spontaneous and exothermic in nature. Phenol desorption from loaded adsorbent was achieved by using 0.1 mol L−1 NaOH, ethanol (100 %) and deionized water.

Synthetic ZrO2 x nH2O was used for phosphate removal from aqueous solution. The optimum adsorbent dose obtained for phosphate adsorption on to hydrous zirconium oxide was 0.1 g. The kinetic process was described very well by a pseudo-second-order rate model. The phosphate adsorption tended to increase with the decrease in pH. The adsorption capacity increased from 61 to 66 mg g(-1) when the temperature was increased from 298 to 338 K. A phosphate desorption of approximately 74% was obtained using water at pH 12.

Carbon xerogel (CX) was used for phenol adsorption from aqueous solution. CX was synthesized by sol–gel polycondensation of resorcinol with formaldehyde using sodium carbonate (Na2CO3) as catalyst. Then, it was dried by convective drying technique and pyrolyzed under inert atmosphere. Phenol adsorption kinetics was very fast, what was attributed to the presence of open pore structure. The kinetic studies showed that the adsorption process could be fitted to a pseudo-second-order model and the particle diffusion process is the rate-limiting step of the adsorption. The phenol removal was maximum and unaffected by pH changes when the initial pH of the phenol solution was in the range of 3–8. The optimum adsorbent dose obtained for phenol adsorption onto CX was 0.075 g/50 cm3 solution. The Langmuir model described the adsorption process better than the Freundlich isotherm model and the monolayer adsorption capacity is 32 mg g−1. Among the desorbing solutions used in this study, the most efficient desorbent was EtOH (100 %) which released about 87 % of phenol bound with the CX.

Activated carbon derived from avocado kernels (AAC) was evaluated for its ability to remove phenol. The Brunauer–Emmett–Teller (BET) surface area of the AAC was 206 m 2 g −1 and the total pore volume was 0.100 cm 3 g −1 . The kinetic of the adsorption process was described by a pseudo-second-order rate model. The maximum uptake was obtained at pH values between 4 and 8.5. The optimum adsorbent dose obtained was 0.1 g. The thermodynamic parameters exhibited the feasibility and the spontaneous nature of the adsorption process. Adsorption isotherms showed that the interaction of phenol with AAC surface was described by a localized monolayer adsorption. The adsorption mechanism was discussed based on experimental results, and the π–π interactions were considered to be an important parameter in the adsorption process. The adsorbent regeneration was investigated using several types of desorbing agents, but no agent show any promising result. The results showed that the prepared activated carbon was an effective adsorbent for phenol removal from aqueous solution.

The kinetic of mullite crystallization from sol–gel method, with different water content, was investigated under non-isothermal conditions using DTA. The sols were obtained from Al(NO3)3.9H2O (ANN) and Si(OC2H5)4 (TEOS) mixtures by varying the water–alcohol content of the system. The crystalline phase changes were verified by X-ray diffraction (XRD). For a sample prepared using ethanol-based alkoxide solution (M0), only Al-poor mullite (p-mullite) crystallizes at 1000 °C; for the one synthesized with low water concentration (M6) Al-rich mullite (r-mullite) and spinel crystallize together; and for a sample prepared using a water-based alkoxide solution only spinel is formed. Thus, the variation of water contents during the synthesis caused great variations in the course of mullitization process. The average value of the apparent activation energy determined for p-mullite, r-mullite and spinel phase crystallization were found to be E = (899 ± 61) kJ mol−1, E = (1015 ± 272) kJ mol−1 and E = (980 ± 196) kJ mol−1, respectively. These results showed that sample M(0) was a monophasic gel, where aluminum and silicon atoms are mixed at a molecular level while sample M(100) was a diphasic gel, where silicon and aluminum atoms are distributed in a nanometric level. The fast reaction between TEOS and water molecules is responsible for this great difference in the sample's homogeneity. The kinetic model of the crystallization process was determined using Malek's procedure. It was established that the crystallization of p-mullite, r-mullite and spinel phase can be described by Sestak–Berggren autocatalytic model.

The adsorption kinetics of phosphate onto Nb2O5·nH2O was investigated at initial phosphate concentrations 10 and 50 mg L−1. The kinetic process was described by a pseudo second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The peak appearing at 1050 cm−1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The effective desorption could be achieved using water at pH 12.

A type of Nb2O5⋅3H2O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-P g−1. The peak appearing at 1050 cm−1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for application to control phosphorus pollution.