Heterogeneous Photocatalysis: Basic Approaches and Terminology

Emeline, Alexei V.; Кузнецов, В. Н.; Ryabchuk, V. K.; Serpone, Nick

doi:10.1016/b978-0-444-53872-7.00001-7

Cited by 13 publications

(12 citation statements)

References 59 publications

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“…Under correct electromagnetic irradiation (E hv ≥ Eg), the semiconductor absorbs this radiation and one electron can be excited from the doping donor level to cd of the semiconductor (equation (5)). In solution, the oxygen molecules adsorbed on the semiconductor surface prevent recombination by trapping electrons and this generates superoxide radical anions (equation (6)) [70,71]. Methylene blue photodegradation proceeds through both parallel and consecutive reactions, as superoxide radical anions can react directly with MB (equation (7)).…”

Section: Optical Studymentioning

confidence: 99%

“…The fact that the KI scavenger decreases about 19% the photodegradation yield indicates that holes (h + ) can be produced in minor proportion after visible absorption, and the redox potential of holes is thermodynamically suitable to oxidize almost any organic molecule. Charge carrier trapping would suppress the recombination and increase the lifetime of the separated electron and hole; other factors such as surface area, crystallinity, and trap density can affect the photocatalytic performance of the semiconductor [70][71][72]:…”

Section: Optical Studymentioning

confidence: 99%

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Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

Vallejo

Cantillo

Díaz‐Uribe

2020

International Journal of Photoenergy

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This study synthesized and characterized Ag-doped ZnO thin films. Doped ZnO powders were synthesized using the sol-gel method, and thin films were fabricated using the doctor blade technique. The Ag content was determined by optical emission spectrometers with inductively coupled plasma (ICP plasma). Additionally, X-ray diffraction, Raman spectroscopy, Atomic Force Microscopy (AFM), diffuse reflectance, and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. Finally, the photocatalytic degradation of methylene blue (MB) was studied under visible irradiation in aqueous solution. The Langmuir-Hinshelwood model was used to determine the reaction rate constant of the photocatalytic degradation. The physicochemical characterization showed that the samples were polycrystalline, and the diffraction signals corresponded to the ZnO wurtzite crystalline phase. Raman spectroscopy verified the ZnO doping process. The AFM analysis showed that roughness and grain size were reduced after the doping process. Furthermore, the optical results indicated that the presence of Ag improved the ZnO optical properties in the visible range, and the Ag-doped ZnO thin films had the lowest band gap value (2.95 eV). Finally, the photocatalytic degradation results indicated that the doping process enhanced the photocatalytic activity under visible irradiation, and the Ag-doped ZnO thin films had the highest MB photodegradation value (45.1%), as compared to that of the ZnO thin films (2.7%).

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Section: Optical Studymentioning

confidence: 99%

Section: Optical Studymentioning

confidence: 99%

Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

Vallejo

Cantillo

Díaz‐Uribe

2020

International Journal of Photoenergy

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“…Generation and recombination of carriers determine the stationary concentration of photogenerated carriers in wide band gap solids (Figure ). Both electrons and holes produced on absorption of photons with energy greater than the band gap energy, E bg , in wide band gap solids initially transit into Franck–Condon states at energies higher than the bottom of the conduction and the top of the valence band, respectively (step 1 in Figure ). Thermal equilibrium between the crystalline semiconductor lattice and the photoproduced carriers is established as a result of relaxation of both energy and momentum of the charge carriers within a time scale of around 100 ps (i.e., 10 –10 s; steps 2 and 2′).…”

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confidence: 99%

Why do Hydrogen and Oxygen Yields from Semiconductor-Based Photocatalyzed Water Splitting Remain Disappointingly Low? Intrinsic and Extrinsic Factors Impacting Surface Redox Reactions

et al. 2016

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Water splitting occurring on a semiconductor photocatalyst has become the Holy Grail process to produce a solar fuel, hydrogen, on irradiation with sunlight (or simulated sunlight) in heterogeneous media. Authors often claim highly efficient evolution of hydrogen and oxygen from water through water splitting or efficient hydrogen evolution in the presence of some sacrificial electron donor, whether photocatalytically or photoelectrochemically. Perusal of the scientific and patent literature reveals that yields of hydrogen are disappointingly low even after decades of remarkable advances in materials science and in strategies to achieve significant progress in water splitting. This Review identifies and discusses intrinsic and extrinsic factors (e.g., Φ hν = fn{β, k r, S, D, d, s, τ, αhν}; photostability; back reactions) that impact redox reactions in general and water splitting in particular. The lack of control and handling of these various factors present a challenging, if not an impossible task in improving process efficiencies to achieve significant practical evolution of hydrogen from water splitting.

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“…where r 0 is the initial reaction rate, c 0 is the initial concentration, k is the reaction rate constant, and K is the apparent equilibrium constant [126].…”

Section: Initial Concentration Of the Reactantmentioning

confidence: 99%

Photocatalysis: Introduction, Mechanism, and Effective Parameters

Veréb

Firak

Alapi

2021

Green Chemistry and Sustainable Technology

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The widely investigated heterogeneous photocatalysis offers an environmentally friendly, efficient, and versatile solution for several environmental problems. Among others, the removal of harmful organic pollutants and the generation of H 2 via water splitting are well-known and most widely studied applications. The process is based on the charge separation caused by the excitation of semiconductor photocatalyst via photon absorption. Due to the intensive development of material science, in addition to the well-known TiO 2 and ZnO, several new semiconductor materials have been designed and synthesized to increase the efficiency of heterogeneous photocatalysis and utilization of solar and/or visible light. This chapter describes the principles and mechanisms of heterogeneous photocatalysis, including the formation of photogenerated charge carriers, the role of different reactive species, and the effect of key parameters on the efficiency.

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Heterogeneous Photocatalysis: Basic Approaches and Terminology

Cited by 13 publications

References 59 publications

Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

Why do Hydrogen and Oxygen Yields from Semiconductor-Based Photocatalyzed Water Splitting Remain Disappointingly Low? Intrinsic and Extrinsic Factors Impacting Surface Redox Reactions

Photocatalysis: Introduction, Mechanism, and Effective Parameters

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