Electron Charge Separation Research Articles

Insights into the Interfacial Charge Transfer Dynamics in Semiconductor–Molecular Catalyst Assemblies for Photo–Induced CO2 Reduction

AbstractThis mini–review summarises examples of photo and photoelectrochemical CO2 reduction reactions (CO2RR) using semiconductor–molecular catalyst–based hybrid assemblies in which studies of charge transfer dynamics were also performed. In these catalysts, the grand challenges are controlling ultra–fast one–electron charge separation and simultaneously governing its impact on the efficiency and product selectivity in the multielectron and multi–proton–assisted CO2RR. In practice, several unwanted electron recombination processes occur in the femtosecond to millisecond timescale range impacting the overall catalysis efficiency. Titanium di‐oxide (TiO2) nanoparticle, mesoporous TiO2 film, copper indium sulphide (CuInS2) quantum dots were used as semiconductor materials, in turn rhenium (I) bipyridine, cobalt (II) terpyridine, cobaloxamine complex, and iron (III) porphyrins were investigated as molecular catalysts. The results of the charge transfer dynamic studies operating in such hybrid systems shed light on their charge accumulation processes, their rate constants for the intramolecular charge transfer processes and the decay lifetimes of the different excited state species that are produced. Moreover, a comprehensive understanding of the catalysts’ charge transfer dynamics is crucial to identifying detrimental charge recombination pathways. These undesired pathways can be used as rational basis for improving the design of future multi–redox–driven hybrid catalysts.

Physico-chemical characterization and photocatalytic activity assessment under UV-A and visible-light irradiation of iron-doped TiO2 nanoparticles

In this work, undoped TiO2 and Fe-doped TiO2 materials as photocatalysts for water remediation, were synthesized using wet chemical methods (sol–gel + precipitation). Their crystalline structure, optical and morphological properties were explored using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopies, UV–vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy coupled to the energy dispersive X-Ray spectroscopy (SEM-EDS). The photocatalytic performance of the synthesized materials was assessed through the degradation of methyl orange (MO) under UV-A and visible-light irradiations. The structural study showed the existence of predominate anatase phase in all synthesized nanomaterials. The optical study showed a widening of the band gap for Fe-doped TiO2 materials and revealed a decrease in charge carrier’s recombination for all Fe-doped TiO2 nanomaterials compared to undoped TiO2. The morphological study confirmed the nanometric scale of the materials particles. The photocatalytic experiments revealed an enhanced photocatalytic activity of 0.5 %wt Fe-doped TiO2, only under UV-A light, compared to the rest of the prepared nanomaterials. The enhanced photocatalytic activity has been attributed to the efficient charge separation of electrons and holes.

Development of a visible-light-active-NiTiO3 coating for the efficient removal of the persistent herbicide 2,6-dichlorobenzamide (BAM) from drinking water

In the present research work, the photocatalytic evaluation of NiTiO3 nanoparticles immobilized on glass plates by the spin-coating procedure was carried out in the degradation of the recalcitrant herbicide 2,6-dichlorobenzamide (BAM). The concentrations of Ni employed to synthesize NiTiO3 nanoparticles were 1 wt% (1TESNi) and 2 wt% (2TESNi). The stability of coatings was evaluated by several washings and thermal treatments, which were verified by UV–vis analyses. The morphology of the coatings was studied by scanning electron microscopy (SEM-EDS). The coatings displayed thickness values of 1.35 and 2.56 μm for TiO2 and 1TESNi, respectively. The crystalline phases of the coatings were analyzed by X-ray diffraction (XRD), confirming the presence of NiTiO3 and other phases related to TiO2. The bandgap of 1TESNi, compared with the bare TiO2, was reduced from 2.96 to 2.40 eV as a consequence of Ni addition. The TiO2, 1TESNi and 2TESNi coatings were evaluated in the photodegradation of BAM using visible-light for 240 min. The highest effectiveness was displayed by the 1TESNi coating, obtaining degradation of 92.56% after 240 min. Also, the photocatalytic efficiency of the 1TESNi coating was only reduced 1.99% after 3 reuse cycles in the BAM degradation. The scavenger tests revealed that the main oxidizing species involved in the reaction were the •OH− and •O2− radicals. The 1TESNi coating showed the highest photocatalytic efficiency because of its absorption in the visible-light region, valuable surface area and electronic charge separation. Thus, these advantageous features guarantee that NiTiO3 coatings are an efficient method for degrading recalcitrant herbicides from drinking water using a practical way to recover and reuse photocatalysts.

Enhanced H2O2 Upcycling into Hydroxyl Radicals with GO/Ni:FeOOH-Coated Silicon Nanowire Photocatalysts for Wastewater Treatment.

There remains continued interest in improving the advanced water oxidation process [e.g., ultraviolet (UV)/hydrogen peroxide (H2O2)] for more efficient and environmentally friendly wastewater treatment. Here, we report the design, fabrication, and performance of graphene oxide (GO, on top)/nickel-doped iron oxyhydroxide (Ni:FeOOH, shell)/silicon nanowires (SiNWs, core) as a new multifunctional photocatalyst for the degradation of common pollutants like polystyrene and methylene blue through enhancing the hydroxyl radical (•OH) production rate of the UV/H2O2 system. The photocatalyst combines the advantages of a large surface area and light absorption characteristics of SiNWs with heterogeneous photo-Fenton active Ni:FeOOH and photocatalytically active/charge separator GO. In addition, the built-in electric field of GO/Ni:FeOOH/SiNWs facilitates the charge separation of electrons to GO and holes to Ni:FeOOH, thus boosting the photocatalytic performance. Our photocatalyst increases the •OH yield by 5.7 times compared with that of a blank H2O2 solution sample and also extends the light absorption spectrum to include visible light irradiation.

Renewable and eco-friendly ZnO immobilized onto dead sea sponge floating materials with dual practical aspects for enhanced photocatalysis and disinfection applications

In this study, we have investigated the role of natural dead sea sponge (DSS, Porifera) as a three-dimensional (3D) porous host substrate for the immobilization of nanostructured ZnO material towards the development of ZnO based floating photocatalysts for efficient removal of methylene blue (MB) dye under the illumination of sunlight. After photodegradation, the treated water after dye degradation contains several pathogens, different disinfectants or chemical reagents that are essentially used. This is not the case for DSS as it can naturally kill any pathogens during the wastewater treatment process. To explore these functions, ZnO nanosheets were incorporated onto DSS via hydrothermal protocol and the as prepared ZnO/DSS hybrid material exhibited approximately ∼100% degradation efficiency for the removal of MB. Importantly, the degradation kinetics associated with the fabricated ZnO/DSS was remarkably accelerated as evidenced by the high values of degradation reaction rate constants (3.35 × 10–2 min−1). The outperformance of ZnO/DSS could be attributed to the adsorption caused by its 3D porous structure together with the high rapid oxidation of MB. Furthermore, the high charge separation of electron–hole pairs, natural porosity, and abundant catalytic sites offered by the hybrid ZnO/DSS floating photocatalyst have enabled quantitative (∼100%) degradation efficiency for MB. Finally, the excellent reusability results confirm the feasibility of using natural ZnO/DSS-based photocatalyst for practical solution of wastewater treatment and other environmental problems.

Enhanced photocatalytic antibacterial and degradation performance by n-p type 0D/2D SnO2−x/BiOI photocatalyst under LED light

The construction of efficient and multifunctional photocatalyst with tight hybridization structure is an ideal method to remove pollutants from wastewater. To achieve the goal, a novel n-p type 0D/2D SnO2−x/BiOI photocatalyst was prepared by using large specific surface area SnO2−x (203.1 m2/g) combining with BiOI nanosheet through a facile in situ growth route. A series of techniques including TEM, HRTEM and BET confirmed the structure of 0D/2D SnO2−x/BiOI composite. As expected, the novel SnO2−x/BiOI photocatalyst can successfully remove tetracycline (TC), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) under LED light. Photocurrent and EIS verified the enhanced separation efficiency of photo-excited electron-hole pairs. Trapping experiment and mass spectrometry analysis revealed the active species, intermediate product and photodegradation pathway in photocatalytic process. The mechanism reveals that the Fermi levels of n-type SnO2−x and p-type BiOI have reached a new equilibrium, which is conducive to charge separation of electrons and holes. This work provides an effective example for the preparation of compact heterojunction photocatalytic materials with high efficiency.

Elucidation of the photocatalytic degradation mechanism of an azo dye under visible light in the presence of cobalt doped TiO2 nanomaterials

In this study, Co–TiO2 nanoparticles were successfully synthesized using sol-gel and precipitation methods. The effect of Co amount on the physicochemical properties of these nanomaterials was investigated using various techniques. The obtained results showed that the structural and optical properties of the synthesized Co–TiO2 nanomaterials depended closely on the weight percent of Co added to TiO2. It was found that, for 1%Co–TiO2, a substitution of Ti4+ and Co2+/Co3+ within the lattice of TiO2 was happened. The results of the photocatalytic degradation of methyl orange (MO) experiments carried out in the presence of the as prepared nanomaterials showed that under visible light, the sample 1%Co–TiO2 exhibited the best MO conversion. The enhanced photocatalytic activity has been attributed to the efficient charge separation of electrons and holes. The mechanistic studies revealed that O2−, h+ and OH are the major active species, and a possible mechanism degradation pathway of MO dye is proposed.

Synthesis and Characterization of Supramolecules of Li + @C60 and Fluorinated Porphyrins

Metal endohedral [60]fullerenes (M@C60) have a unique structure encapsulating a metal atom (M) inside the π−conjugated spherical C60 cage. Lithium cation endohedral fullerene (Li + @C60) is a commercially available M@C60 and has a potential for application in nano material fields. The cationic Li+@C60 crystallizes with weakly coordinated anions such as SbCl6 − [1], PF6 − [2], Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion (TFPB−) [3], and bis(trifluoromethanesulfonyl)imide anion (TFSI−) [3]. Due to the inside Li+ cation, the first reduction potential of Li+@C60 is shifted to positive direction by 0.7 eV than that of pristine C60. As a result, Li+@C60 has larger electron acceptability than C60 [1]. Li+@C60 also forms a guest–host type supramolecule with [10]cycloparaphenylene ([10]CPP) [4] and π−π stacking supramolecules with porphyrins or phthalocyanines [5][6]. A supramolecule of Li+@C60 and 5,10,15,20-tetrakis(4–sulfonatophenyl) zinc porphyrin anion (ZnTPPS4 –), [Li+@C60 – ZnTPPS4 –] with the binding constant of ca. 105 M– 1 shows a long−lived electron charge separation state by photoinduced electron transfer and can be used in photovoltaic cells [5]. The [Li+@C60 – ZnTPPS4 –] based photovoltaic cell shows maximum incident photon-to-photocurrent efficiency (IPCE) value of 78% under the certain condition [7]. The performance of the photovoltaic cells would be changed by the chemical modification of porphyrins.Here, we synthesized two kinds of porphyrins to obtain new supramolecules of Li+@C60. The first one is neutral 5,10,15,20-Tetrakis(1,2,4,5-tetrafluorophenyl) porphyrin (H2TTFPP). H2TTFPP was synthesized by Lindsey method and characterized by 1H NMR, 19F NMR, UV-vis, CV, DPV, and XRD. The second one is anionic 5,10,15,20-Tetrakis(4-carboxymethylthio-2,3,5,6-tetrafluorophenyl) zinc porphyrin tetrabutylammonium (ZnTFPP4TC4 −4TBA+). ZnTFPP4TC4 −4TBA+ was synthesized according to the modified Lourenço method [8] and characterized by 1H NMR, 19F NMR, UV-vis, CV, and DPV.H2TTFPP was confirmed to form supramolecular structure with Li+@C60 in the co-crystal by X-ray structure analysis. ZnTFPP4TC4 − was confirmed to form a supramolecule with Li+@C60 in solution by UV-vis titration experiment. The binding constant of [ZnTFPP4TC4 − − Li+@C60] is significantly larger than that of [H2TTFPP − Li+@C60] because of strong coulomb interactions between anionic ZnTFPP4TC4 − and cationic Li+@C60.

Preparation of Cu3N/MoS2 Heterojunction through Magnetron Sputtering and Investigation of Its Structure and Optical Performance.

Cu3N/MoS2 heterojunction was prepared through magnetron sputtering, and its optical band gap was investigated. Results showed that the prepared Cu3N/MoS2 heterojunction had a clear surface heterojunction structure, uniform surface grains, and no evident cracks. The optical band gap (1.98 eV) of Cu3N/MoS2 heterojunction was obtained by analyzing the ultraviolet-visible transmission spectrum. The valence and conduction band offsets of Cu3N/MoS2 heterojunction were 1.42 and 0.82 eV, respectively. The Cu3N film and multilayer MoS2 formed a type-II heterojunction. After the two materials adhered to form the heterojunction, the interface electrons flowed from MoS2 to Cu3N because the latter had higher Fermi level than the former. This behavior caused the formation of additional electrons in the Cu3N and MoS2 layers and the change in optical band gap, which was conducive to the charge separation of electrons in MoS2 or MoS2 holes. The prepared Cu3N/MoS2 heterojunction has potential application in various high-performance photoelectric devices, such as photocatalysts and photodetectors.

Visible‐Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation

AbstractResearch on the photochemical reduction of CO2, initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high‐volume chemicals whose dehydrogenation is of interest, so the coupling of a CO2 photoreduction to a hydrocarbon‐photodehydrogenation reaction seems a worthwhile concept to explore. A three‐component construct was prepared including graphitic carbon nitride (g‐CN) as a visible‐light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole–electron charge separation, and an electron donor to a rhenium‐based CO2 reduction catalyst. Upon photoactivation of g‐CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible‐light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium‐based catalyst active for the selective reduction of CO2 to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS). An experimental Z‐scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.

Plasmonic Au nanoparticle-decorated Bi2Se3 nanoflowers with outstanding electrocatalytic performance for hydrogen evolution

Hydrogen production from water splitting through electrocatalytic or photoelectrochemical route shows great potential for renewable energy conversion. Herein, the plasmon-enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by Au nanoparticle-decorated Bi2Se3 nanoflowers (Au@Bi2Se3 NFs) as catalysts for hydrogen evolution reaction (HER), leading to a more than 3-fold increase of current under excitation of Au localized surface plasmon resonance (LSPR) and affording a markedly decreased overpotential of 375 mV at a current density of 10 mA cm−2. The HER enhancement can be largely attributed to effective electron-charge separation and the increase of carrier density in Bi2Se3 induced by the injection of hot electrons of Au nanoparticles. Meanwhile, Bi2Se3 nanoflowers (NFs), a kind of topological insulators, possess gapless edges on boundary and show metallic character on surface, providing a path for the flow of electrons in the electrocatalytic system. This study opens up a new avenue towards the design of higher energy conversion catalytic water splitting systems with the assistance of light energy, which could increase of HER catalysis efficiency by plasmonic excitation.

First principles computational study on hydrolysis of hazardous chemicals phosphorus trichloride and oxychloride (PCl3 and POCl3) catalyzed by molecular water clusters

Using first principles calculations we unveil fundamental mechanism of hydrolysis reactions of two hazardous chemicals PCl3 and POCl3 with explicit molecular water clusters nearby. It is found that the water molecules play a key role as a catalyst significantly lowing activation barrier of the hydrolysis via transferring its protons to reaction intermediates. Interestingly, torsional angle of the molecular complex at transition state is identified as a vital descriptor on the reaction rate. Analysis of charge distribution over the complex further reinforces the finding with atomic level correlation between the torsional angle and variation of the orbital hybridization state of phosphorus (P) in the complex. Electronic charge separation (or polarization) enhances thermodynamic stability of the activated complex and reduces the activation energy through hydrogen bonding network with water molecules nearby. Calculated potential energy surfaces (PES) for the hydrolysis of PCl3 and POCl3 depict their two contrastingly different profiles of double- and triple-depth wells, respectively. It is ascribed to the unique double-bonding O=P in the POCl3. Our results on the activation free energy show well agreements with previous experimental data within 7kcalmol−1 deviation.

Insights into the Hole Blocking Layer Effect on the Perovskite Solar Cell Performance and Impedance Response

The implementation of efficient hole blocking layers (BLs) is of vital importance to achieve high efficiency in solar cells using organolead trihalide materials as the solar light absorber. BLs permit electronic charge separation and avoid the recombination of charges by blocking the hole transfer to the anode. In this study, BLs have been prepared by aerosol spray pyrolysis and spin-coating using various solution compositions. The morphological, optical, microstructural and crystalline properties as well as the phase composition of these layers have been characterized by scanning electron microscopy, Raman spectroscopy, and optical measurements. Their blocking ability has been evaluated by cyclic voltammetry. A strong relationship has been found between these properties and the solar cell J–V characteristics and performances. Overall, we figured out that the sprayed BLs were thin, highly compact, covering, and conformal. No cracks or pinholes were found because the precursor underwent degradation and con...

Ab initio study of structural and electronic properties of single crystal and core/shell II-VI semiconductor nanowires

Structural and electronic properties of pristine and H-passivated wurtzite type ZnSe, ZnTe nanowires and ZnX/ZnY (X=Se(Te) and Y=Te(Se)) core/shell nanowires oriented along the [0001] direction have been investigated using first-principles calculations. The changes in the electronic structure of the nanowires due to the quantum confinement and morphology have been searched. Quantum confinement increases the band gap energy as the diameters of ZnSe and ZnTe nanowires decrease. Both homostructured and heterostructured nanowires are found to show a semiconducting character with direct band gaps at Γ-point. Changing the morphology from homostructured nanowires to heterostructured core/shell nanowires has an important impact on the electronic structure. For instance, the charge separation of electrons and holes along the infinite direction of core/shell nanowires shows a strong preference for electron(hole) states localized inside ZnSe(ZnTe) regions.

Spin–charge separation of dark-state polaritons in a Rydberg medium

The propagation of light fields through a quasi one-dimensional cold atomic gas, exciting atomic Rydberg levels of large principal quantum number under conditions of electromagnetically induced transparency, can lead to a stable two-mode Luttinger liquid system. Atomic van der Waals interactions induce a coupling of bosonic field modes that display both photonic and atomic character, the Rydberg dark-state polaritons (RDPs). It is shown that by tunable control of the van der Waals coupling, the RDP may decouple into independent ‘spin’ and ‘charge’ fields which propagate at different speeds, analogous to spin–charge separation of electrons in a one-dimensional metal.

Photoelectrochemical Ion Pumping with Dye-Functionalized Polymer Membranes

Artificial photosynthesis could be a cost-effective and sustainable means of converting sunlight energy into usable energy. Most artificial photosynthetic systems mimic nature’s properties of light absorption, electronic charge separation, and electronic charge collection, where ultimately electrons make and break chemical bonds. However, nature also transduces photon energy into proton gradients whose electric potential also drives chemical-bond formation. In my presentation I will report on my research group’s progress toward mimicking nature in function, by using light to drive endergonic proton transfer, ultimately converting photon energy into ionic current. The applicability and practicality of this material as a membrane in solar fuels devices and as a separate ionic photoelectrochemical device will also be discussed. My research group’s near-term goal is to provide a proof-of-concept demonstration of an artificial proton pump where light-driven ion transport results in photovoltaic action. For an initial model system we utilized a conical nanopore etched in a polyethylene terephthalate plastic sheet. This pore was formed via swift heavy ion bombardment followed by alkaline chemical etching which resulted in a pore lined with fixed anionic functional groups. Then, using peptide coupling chemistries, the pore was asymmetrically functionalized with novel photoacids to generate a region containing fixed cationic dyes. This ordered distribution of interfacial charge was intended to mimic a solid-state semiconductor pn-junction and be used to separate photogenerated charges. We demonstrated that under visible-light illumination and a small reverse bias, excitation of the photoacid molecules resulted in an ionic photocurrent. We are currently expanding this initial research and successful demonstration of an artificial light-driven ion pump to other polymeric materials with hopes of generating ionic power through sunlight absorption and incorporating these materials as ion-exchange membranes in solar fuels devices.

Improved photocatalytic activity in RuO2–ZnO nanoparticulate heterostructures due to inhomogeneous space charge effects

New 2-6 wt% RuO2-ZnO heterojunction nanocatalysts were synthesized by a straightforward two-step procedure. They were composed of a porous network of aggregated 25 nm wurtzite ZnO nanocrystallites modified with RuO2 and showed enhanced light absorption in the visible region due to surface plasmon resonance. In order to investigate the energetic structure of the photocatalyst XPS core line and valence band spectra of in situ in UHV prepared heterointerfaces were compared to results obtained from the particles. The shift of Zn 2p3/2 and O 1s core level spectra was determined to be at least 0.80 ± 0.05 eV for the in situ prepared heterojunction whereas it was found to be 0.40 ± 0.05 and 0.45 ± 0.05 eV, respectively, in the photocatalysts. The different values were ascribed to the reduced size of the particles and the different measurability of band bending at the interface of the heterojunction RuO2-ZnO compared to the nanoparticles. The RuO2/ZnO photocatalysts showed higher photocatalytic activity and recyclability than pure ZnO for the degradation of various dyes under UV light irradiation due to vectorial charge separation of photogenerated electrons and holes resulting from internal electric field, the ruthenium oxide acting as a quasi-metallic contact.

Multidimensional ion-acoustic solitary waves and shocks in quantum plasmas

The nonlinear theory of two-dimensional ion-acoustic (IA) solitary waves and shocks (SWS) is revisited in a dissipative quantum plasma. The effects of dispersion, caused by the charge separation of electrons and ions and the quantum force associated with the Bohm potential for degenerate electrons, as well as, the dissipation due to the ion kinematic viscosity are considered. Using the reductive perturbation technique, a Kadomtsev–Petviashvili–Burgers (KPB)-type equation, which governs the evolution of small-amplitude SWS in quantum plasmas, is derived, and its different solutions are obtained and analyzed. It is shown that the KPB equation can admit either compressive or rarefactive SWS according to when H≶2/3, or the particle number density satisfies n0≷1.3×1031cm−3, where H is the ratio of the electron plasmon energy to the Fermi energy densities. Furthermore, the properties of large-amplitude stationary shocks are studied numerically in the case when the wave dispersion due to charge separation is negligible. It is also shown that a transition from monotonic to oscillatory shocks occurs by the effects of the quantum parameter H.

Hollow shaped nanofibers with (Ti, Sn)O2 solid-solutions: Synthesis, characterization, and photocatalytic application

Novel hollow shaped nanofibers with (Ti, Sn)O2 solid-solutions have been synthesized for photocatalysts by the impregnation method using tin chloride (SnCl2) and titanium tetraisopropoxide (TTIP), and further characterized by SEM, EDS, TGA, and XRD. The results showed that uniformly distributed hollow shaped nanofibers with (Ti, Sn)O2 solid-solutions was successfully formed in the case of the optimum weight ratio of the Ti precursor. These hollow shaped nanofibers exhibited the higher photocatalytic reactivity by the conversion of methylene blue in aqueous solution under UV irradiation than not only prepared SnO2 but also TiO2 hollow shaped nanofibers. The highest degradation ratio was about 85% at 70min using hollow shaped nanofibers with (Ti, Sn)O2 solid-solutions photocatalysts, which exhibited more than 3.5 times that of TiO2. It has been found that enhanced MB degradation efficiency is not only due to the charge separation of electron–hole pairs but also increasing the photocatalytic reactive site.

Density matrix treatment of non-adiabatic photoinduced electron transfer at a semiconductor surface

Photoinduced electron transfer at a nanostructured surface leads to localized transitions and involves three different types of non-adiabatic couplings: vertical electronic transitions induced by light absorption emission, coupling of electronic states by the momentum of atomic motions, and their coupling due to interactions with electronic density fluctuations and vibrational motions in the substrate. These phenomena are described in a unified way by a reduced density matrix (RDM) satisfying an equation of motion that contains dissipative rates. The RDM treatment is used here to distinguish non-adiabatic phenomena that are localized from those due to interaction with a medium. The fast decay of localized state populations due to electronic density fluctuations in the medium has been treated within the Lindblad formulation of rates. The formulation is developed introducing vibronic states constructed from electron orbitals available from density functional calculations, and from vibrational states describing local atomic displacements. Related ab initio molecular dynamics calculations have provided diabatic momentum couplings between excited electronic states. This has been done in detail for an indirect photoexcitation mechanism of the surface Ag(3)Si(111):H, which leads to long lasting electronic charge separation. The resulting coupled density matrix equations are solved numerically to obtain the population of the final charge-separated state as it changes over time, for several values of the diabatic momentum coupling. New insight and unexpected results are presented here which can be understood in terms of photoinduced non-adiabatic transitions involving many vibronic states. It is found that the population of long lasting charge separation states is larger for smaller momentum coupling, and that their population grows faster for smaller coupling.