New carbon xerogel-TiO2 composites with high performance as visible-light photocatalysts for dye mineralization

doi:10.1016/j.apcatb.2016.08.015

Applied Catalysis B: Environmental

Volume 201, February 2017, Pages 29-40

https://doi.org/10.1016/j.apcatb.2016.08.015 Get rights and content

Highlights

•
Carbon xerogels-TiO₂ composites were prepared by sol-gel synthesis.
•
TiO₂ nanoparticles are highly and homegeneously dispersed on the carbon matrix.
•
Carbonization induces the formation of oxygen vacancies.
•
The synergetic behaviour provokes band gap tuning and photocatalytic activity under visible light.
•
Dye is totally mineralized avoiding toxicity in water.

Abstract

A series of carbon xerogels-TiO₂ samples was prepared by sol-gel synthesis, modifying the synthesis procedure to have carbon-TiO₂ composite or TiO₂-coated materials. Textural, morphological and chemical properties were extensively characterized and correlated with the photocatalytic activity. In the case of composites, a homogeneous and highly mesoporous structure is formed, where the intimate contact between both phases allows a high and homogeneous dispersion of TiO₂ nanoparticles. During carbonization, the formation of oxygen vacancies is favoured, but the transition anatase to rutile is avoided by the carbon matrix. In the case of coated samples, microporous materials structured as microspheres were obtained, TiO₂ present a greater crystal size and some transformation to rutile. The synergetic role of carbon phase and the formation of oxygen vacancies in the TiO₂-phase contribute to narrow the composite band gap in such a manner that all samples are active under visible radiation reaching the total mineralization of the pollutant and the elimination of the toxicity.

Graphical abstract

Introduction

The increasing pollution level of water resources together with the appearance of new and more stable pollutant in solution (emerging pollutant) make necessary the development of new and more efficient protocols to deal with this new problem. Traditionally, environmental catalysis tries to respond adequately to this requirement, fitting or developing materials and processes for a progressively more industrialized society. A large battery of advanced oxidation processes (Fenton, ozonation, catalytic wet air oxidation (CWAO), etc) is being developed [1], [2], [3]. Between them, photocatalytic processes are very interesting, and sometimes are used in combination [4] with the previous ones (photoFenton, photoozonation, etc). Photocatalytic processes become especially interesting when are able to use the visible radiation, not only by the energy saving, but because in such a way can be easily used in developing countries.

It is well known that TiO₂ is the most extensively used photocatalyst. It has been regarded as an efficient photocatalyst for degradation of organic pollutants from water due to its high stability, low cost and environmental friendliness [5], [6]. However, UV-light is necessary to create the hole-electron pairs needed for the photocatalytic reaction which limits their use in environmental applications. Only 3–5% of UV in solar spectrum can be absorbed by pure TiO₂ due to its wide band gap (3.2 eV of anatase and 3.0 eV of rutile), which greatly restricts its photocatalytic applications in the visible-light range [7], [8].

Therefore, to improve the efficiency of TiO₂ under solar (or visible) light is necessary to modify the material in order to facilitate the visible light absorption. Several approaches are made with this aim such us the introduction of doping agents or sensitizers to decrease the material band gap [9], [10]. The introduction of metal doping agents into TiO₂ narrows the band gap by producing new hybrid states which confer significant visible light absorbance to TiO₂. On the other hand, the improvement obtained using sensitizers is due to the direct absorption of visible light by the sensitizer and the release of electrons to TiO₂ in a redox process.

However, different problems were also detected. Metal doping shows thermal instability of doped TiO₂, electron trapping by the metal centres decreasing the photocatalytic activity and high processing costs [11], [12]. Alternatively, doping with non-metals such as N and S are used [13], [14] being now the main drawbacks (i) the difficulty to obtain N-doped TiO₂ with high nitrogen concentration; (ii) the formation of defects which can act as recombination centres for carriers [15]; and (iii) the decrease of N concentration at the surface layer after irradiation [16].

The synergetic effect of the addition of carbon materials to TiO₂ photocatalysts was initially presented using directly simple mixtures of both solids [17], [18]. Although activated carbons were initially used to enhance the TiO₂ photocatalytic performance [19],nanocarbons including carbon nanotubes (CNT) [18], nanohorms, fullerenes and graphene [20], [21] have been combined with TiO₂ by different approach for such objective. Carbon gels are a new type of nanocarbons [22] with high potential applications in catalysis due to their unique properties [23]. In spite that some carbon gels −TiO₂ composites were previously described [24], until our knowledge they have not been used today as photocatalysts.

The incorporation of carbon materials to the photocatalyst improve the TiO₂ photoactivity by different mechanism [25]: (i) carbon absorbs over a wide range of visible light producing band-gap tuning/photosensitization, (ii) minimisation of electron/hole recombination and (iii) promotion of the reactants adsorption. The higher porosity of carbon facilitates the titania dispersion and the adsorption of reactants, enhancing the active site number and the contact between reactants and catalysts [25]. Additionally, carbon is a good electron acceptor. Electron transfers to the carbon phase minimize the electron/hole recombination on the TiO₂. Also the better dispersion of the semiconductor nanoparticles on the carbon phase reduce that recombination because mainly occurs at boundaries and defects [26]. Thus, if the particle size is reduced, the distance that the photogenerated electrons and holes need to travel through the surface reaction sites is reduced, thereby decreasing the recombination probability [27].

In this paper, new TiO₂-carbon composites were prepared by a sol–gel process and the xerogels obtained were deeply characterized and tested in the degradation of organic pollutants under visible light. The photocatalytic activity of the composites was evaluated using Orange G (OG) as a target molecule, and the relationship of the photocatalytic activity with the physicochemical characteristics of composites was studied. The prepared new materials present a high performance for the complete mineralization of pollutants (OG) under visible light.

Section snippets

Synthesis of TiO₂-carbon xerogel composites

TiO₂-carbon xerogel composites were prepared by sol-gel synthesis using resorcinol-formaldehyde and titanium isopropoxide (IV) as carbon and titanium oxide precursor, respectively, in the presence of a non-ionic surfactant (Span 80). In a typical synthesis procedure, Span 80 (S) was dissolved in 900 mL of n-heptane and heated at 70 °C under reflux and stirring (450 rpm). Then a mixture containing resorcinol (R), formaldehyde (F) and water (W) was added dropwise into the above solution. Immediately

Results and discussion

The fraction of TiO₂ present in the CTiX carbon composites was determined by TGA, after burning the carbon phase in air flow. The TiO₂ percentages are slightly higher than the theoretical ones due to the fact that the weight lost during the carbonization is not exactly 50%, however the experimental data are much closed to the expected ones (Table 1). Morphology of sample was studied by scanning electron microscopy (Fig. 2). CTiX samples (Fig. 2a) show a typical structure of carbon xerogels [39]

Conclusions

Carbon xerogel-TiO₂ composites (CTiX) were successfully synthesized by sol-gel techniques. Composites present a homogeneous and three-dimensional mesoporous structure, where both phases are also homogenously and intimately distributed. This procedure can be fitted to obtain TiO₂ coating the carbon phase structured microspheres, obtaining microporous materials. Due to the interactions between both phases all composites present a high dispersion of anatase TiO₂ nanoparticles on the carbon support

Acknowledgements

EBG acknowledges for a pre-doctoral fellowship to the MCINN project CTM2010-18889. This research is supported by the FEDER and Spanish projects CTQ2013-44789-R (MINECO) and P12-RNM-2892 (Junta de Andalucía).

References (58)

F. Rojas-Serrano et al.
Chem. Eng. Process.
(2016)
B.M. Esteves et al.
J. Environ. Manag.
(2016)
R.S. Ribeiro et al.
Appl. Catal. B: Environ.
(2016)
J. Guzmán et al.
Sep. Purif. Technol.
(2016)
M. Pelaez et al.
Appl. Catal. B: Environ.
(2012)
W. Ren et al.
Appl. Catal. B: Environ.
(2007)
Y. Wang et al.
Thin Solid Films
(1999)
C. Di Valentin et al.
Chem. Phys.
(2007)
J. Matos et al.
Appl. Catal. B: Environ.
(1998)
W. Wang et al.
Appl. Catal. B: Environ.
(2005)

G. Li Puma et al.

J. Hazard Mater

(2008)

S. Morales-Torres et al.

Appl. Surf. Sci.

(2013)

M.J. Sampaio et al.

Appl. Catal. B: Environ.

(2015)

M. Inagaki et al.

Carbon

(2004)

F.J. Maldonado-Hódar

Catal. Today

(2013)

F.J. Maldonado-Hódar et al.

Appl. Catal. A: Gen.

(2000)

R. Leary et al.

Carbon

(2011)

E. Gallegos-Suárez et al.

Chem. Eng. J.

(2012)

M.M. Dubinin

Carbon

(1985)

R. Ubago-Pérez et al.

Microporous Mesoporous Mater.

(2006)

F. Orellana-García et al.

Appl. Catal. B: Environ.

(2016)

C.H. Yang

J. Colloid Interface Sci.

(1998)

C. Moreno-Castilla et al.

Carbon

(2005)

T. Potlog et al.

Curr. Appl. Phys.

(2016)

A.R. Gonzalez-Elipe et al.

Stud. Surf. Sci. Catal.

(1989)

A.R. González-Elipe et al.

J. Catal.

(1991)

L.M. Pastrana-Martínez et al.

Appl. Catal. B: Environ.

(2014)

S. Monticone et al.

Appl. Surf. Sci.

(2000)

A. Moya et al.

Appl. Catal. B: Environ.

(2015)

Cited by (85)

Open-cell ceramic foams covered with TiO<inf>2</inf> for the photocatalytic treatment of agro-industrial wastewaters containing imazalil at semi-pilot scale
2023, Journal of the Taiwan Institute of Chemical Engineers
Imazalil is a fungicide widely used in postharvest agroindustry, which causes a negative impact on the environment. To remove it from agro-industrial wastewaters, solar heterogeneous photocatalysis, with the photocatalyst fixed onto support, constitutes a promising technique. In this work, two open-cell ceramic foams (with and without carbon) were evaluated as TiO₂ supports. Technical and economic feasibility of photocatalysis with TiO₂ supported on ceramic foams were assessed.
Foams were covered with TiO₂ by dip-coating and subsequent calcination. The obtained systems were characterized by different techniques. Lab-scale removal of imazalil in pure and real water matrices was studied for both materials. The highest performance system was also evaluated at semi-pilot scale.
The C-free support led to the highest photoactivity in both water matrices at lab-scale. No TiO₂C synergistic effect was observed due to photon absorption phenomena detected for the support with graphite. The C-free foams coated with TiO₂ can be used in solar reactors to decontaminate wastewater with imazalil, achieving 95% degradation and a nontoxic condition for Allivibrio fischeri bacteria at accumulated energy values less than 10 kJ·L⁻¹. This technique can be adapted to each real situation through the adequate selection of the number of photocatalytic converters exposed to sunlight. After economic evaluation, the experimental technology could be considered cost-effective.
Sunlight-active hierarchical Ag@insulator@ZnO core-shell array based on natural diatoms for environmental remediation
2023, Applied Materials Today
A nature inspired plasmonic core-shell architecture was proposed by incorporating a natural siliceous insulator shell (Navicula salinicola frustules) in Ag/diatomite/ZnO hierarchical nanostructures to overcome the recombination of energetic charge carriers (e⁻/h⁺), corrosion of bare metal, and to facilitate the composite separation after reaction. The photocatalytic performance of the as-prepared composites, monitored by decomposition of methylene blue (MB), was investigated under both UV and simulated sunlight irradiation. Ag/diatomite/ZnO exhibited efficient photocatalytic performance (near 100% degradation and 95% mineralization) under simulated sunlight irradiation with apparent rate constant of 0.0246 min⁻¹, which was found to follow pseudo-first order kinetics. The enhanced photocatalysis action of metal/insulator/semiconductor as compared to metal/semiconductor and the semiconductor alone could be ascribed to the synergistic effects of the photonic structure of regular frustules, improved sunlight harvesting efficiency, suppressed back electron transfer, and prohibited oxidization of Ag. While the as-synthesized composite was easy to separate from the reaction, however, it was in the throes of losing the photocatalytic activity after three rounds of reuse. A possible mechanism of photocatalytic degradation of MB induced by Ag/diatomite/ZnO under sunlight irradiation was proposed based on dye degradation measurements and reactive species trapping experiments. While the reusability of as-prepared composite will doubtless be much scrutinized, our study may provide a new insight into the design and fabrication of plasmonic-based nanomaterials for use in industry applications under solar light illumination.
Synthesis of a reusable magnetic photocatalyst based on carbon xerogel/TiO<inf>2</inf> composites and its application on acetaminophen degradation
2022, Ceramics International
Citation Excerpt :
Such disadvantages can be reversed through association with a carbon matrix, such as graphenes, nanotubes, graphitic carbon nitride, or carbon xerogels (CX) [14]. The carbon matrix presents a high surface area which can improve the substrate adsorption and is the first step in the degradation process, leading to improvement in photocatalytic activity [15–18]. Carbon nanomaterials offer unique advantages such as chemical inertness, stability, absorptivity, and modifiable structural and electrical properties.
This work describes the production photocatalyst in two steps, (1) production of N-CXTi nanocomposites by sol-gel polymerization of resorcinol-formaldehyde-melamine in the presence of K₂TiF₆ inorganic metallic salt with TiO₂ as precursor; (2) Synthesis of the Fe₃O₄/N-CXTi and Fe₃O₄/SiO₂/N-CXTi nanocomposites by mechanical mixing of N-CXTi and magnetic nanoparticles. The magnetic nanoparticles (Fe₃O₄ and Fe₃O₄/SiO₂) were prepared by a chemical co-precipitation method and subsequent functionalization by silica (SiO₂). The materials were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, X-ray diffractometry, and textural properties. The composites presented a morphology heterogeneous structure and the presence of two phases for the introduction of TiO2. The region was formed by amorphous carbon and carbon spheres, where Ti is detected only immersed in the amorphous carbon particles, in the anatase and rutile phase, and the presence of magnetic nanoparticles is located surrounded by the carbon structure. Results for the recovery and reuse of the photocatalyst Fe₃O₄/SiO₂/N-CXTi presented the highest efficiency in the removal of the acetaminophen (APP) in the aqueous medium; the result of the reaction carried out in the presence of ultraviolet irradiation showed that the magnetic photocatalyst removed 99.2% of APP in an aqueous medium. Results for the recovery and reuse of the photocatalysts for nine consecutive reactions showed that they can be separated from the reaction medium in a simple and fast way, without significant losses of photocatalytic efficiency and excellent recovery of the photocatalyst.
Guar gum-driven high-energy plasma electrolytic oxidation for concurrent improvements in the electrochemical and catalytic properties of Ti-15 Zr alloy
2022, Surfaces and Interfaces
A hybrid composite layer with optimal chemical stability and catalytic activity was formed on Ti-15 Zr alloy for the first time via high-energy plasma electrolytic oxidation driven by guar gum (GG). Here, the substrate was treated in a phosphate-based electrolyte containing GG (0, 1, 1.5, and 2 g/L), which might act as an electron donor during plasma-assisted electrochemical processes. The ability of GG molecules to form an adsorption layer on the substrate surface through either polar –OH or hetero-oxygen atoms would be responsible for the reduction in the intensity of plasma discharges observed at lower concentrations of GG (1 g/L). However, higher concentrations of GG would act as barriers to the electron avalanche by accumulating at the surface of the barrier passive layer developed on the substrate surface. As a result, the discharges in the 1.5GG and 2GG samples were more potent than those observed in other electrolytes to overcome the electron avalanche obstruction. In addition, the chemical incorporation of ZrO₂ into the TiO₂ layer would be affected by the GG additive, which would donate electrons to the oxygen bubble, acting as electron acceptors in the electrolyte. The chemical stability of the 1.5GG sample was superior to the other samples as it had the highest values of outer and inner layer resistances (1.79 × 10⁷ and 4.81 × 10⁷ Ω.cm², respectively). The 1.5 GG sample achieved also a relatively good catalytic activity of 95.97% toward methylene blue. Thus, a multifunctional layer with high chemical stability and high catalytic activity was formed, which would be associated with the presence of rutile and ZrO₂ in the coatings, respectively. The obtained results of the oxide layers were very high and comparable to other works.
Recent advances in carbonaceous sustainable nanomaterials for wastewater treatments
2022, Sustainable Materials and Technologies
The challengeable situation prevailing throughout the world is still a question mark regarding safe drinking and cleaning for water, and therefore to be resolved on priority basis in concerning research area. In this regard, advancement of environment-friendly supportable nanomaterials possessing unique benefits such as superior efficiency and selectivity, rich earth-abundance, good recyclability, low-cost producing agency, and achievable stability has become a top priority despite several prominent challenges as well as constraints remaining still unresolved. Carbonaceous nanomaterials especially like activated carbon, multi-walled carbon nanotubes, single-walled carbon nanotubes, and carbon quantum dots have been developed and their application as adsorbents toward wastewater treatment anchored with its purification; graphene (GR) and graphene oxide (GO) derivatives and other carbon-derivative nanomaterials like graphitic carbon nitrides as well as carbon sponges/aerogels have imparted significant contribution for water associated with wastewater treatment and remediation (adsorption, membrane technologies, advanced oxidation processes), especially on the industrial level along with pharmaceutical-laden wastages. This review envelopes developed technologies, methodologies, and surface modifications regarding carbonaceous nanomaterials for removal of pollutants along with ionic metals in an aqueous medium, and proving novelty regarding nanoadsorbents for a variety of issues such as wastewater, drinking water, and groundwater remediation. Additionally, heterojunctions strategies are also addressed with current alarming trends and resolvable challenges pertaining to sustainable carbon and its derivatives unified with substantial appliances while handling and purifying wastewater are suggestively highlighted.
Resorcinol-based carbon xerogel/ZnO composite for solar-light-induced photodegradation of sulfamerazine
2022, Optical Materials
Recently, the release of antibiotics, such as sulfonamides, into the environment has raised significant concern due to the potential creation of antibiotic-resistant bacteria. Thus, the development of remediation technologies for effluents containing such compounds is of utmost urgency. In this context, this work evaluated the creation of a resorcinol-based carbon xerogel/zinc oxide photocatalyst (XC/ZnO) to efficiently promote the photodegradation of the antibiotic known as sulfamerazine in aqueous media. The employment of this carbonaceous structure as a co-catalyst is justified by its high surface area and electrical conductivity. The methodology used in the synthesis of the composites was a simple one-pot reaction, combining the simultaneous precipitation of zinc oxide and polycondensation of the resorcinol-based carbon gel. Regarding the composites' characterization, X-ray diffractometry confirms that the composites have the Wurtzite structure of the zinc oxide, whereas the carbon xerogel formation is evidenced by the infrared, diffuse reflectance, and X-ray photoelectron spectroscopies. Morphology-wise, the XC/ZnO is arranged as nodular particle agglomerates, with particles between 500 nm and 50 nm. The photocatalytic tests under simulated solar radiation show that the composites developed are superior to the pure oxide in the photodegradation of sulfamerazine, as all XC/ZnO materials developed achieved higher apparent reaction rate constants (k_app) than pure zinc oxide, with the XC/ZnO 0.5 material obtaining a k_app 75% higher than the one observed for the ZnO sample. Furthermore, the chronoamperometry tests confirmed that the optimized composite (XC/ZnO 0.5) has a greater capacity for photocurrent generation when compared to pure zinc oxide. Therefore, the modification proposed was successful to enhance the photodegradation of sulfamerazine in aqueous media, highlighting the viability of the composites developed for photocatalytic applications.

View all citing articles on Scopus

View full text

New carbon xerogel-TiO2 composites with high performance as visible-light photocatalysts for dye mineralization

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of TiO2-carbon xerogel composites

Results and discussion

Conclusions

Acknowledgements

Chem. Eng. Process.

J. Environ. Manag.

Appl. Catal. B: Environ.

Sep. Purif. Technol.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Thin Solid Films

Chem. Phys.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

J. Hazard Mater

Appl. Surf. Sci.

Appl. Catal. B: Environ.

Carbon

Catal. Today

Appl. Catal. A: Gen.

Carbon

Chem. Eng. J.

Carbon

Microporous Mesoporous Mater.

Appl. Catal. B: Environ.

J. Colloid Interface Sci.

Carbon

Curr. Appl. Phys.

Stud. Surf. Sci. Catal.

J. Catal.

Appl. Catal. B: Environ.

Appl. Surf. Sci.

Appl. Catal. B: Environ.

New carbon xerogel-TiO₂ composites with high performance as visible-light photocatalysts for dye mineralization

Synthesis of TiO₂-carbon xerogel composites