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This study reports the solar light-driven activation of a bicyclic aminoxyl mediator to achieve C–C bond cleavage of a lignin model compound at room temperature using a donor–π-conjugated bridge–acceptor organic dye-based photoelectrochemical system.

The selective cleavage of C-C/C-O linkages represents a key step toward achieving the chemical conversion of biomass to targeted value-added chemical products under ambient conditions. Using photoelectrosynthetic solar cells is a promising method to address the energy intensive depolymerization of lignin for the production of biofuels and valuable chemicals. This feature article gives an in-depth overview of recent progress using dye-sensitized photoelectrosynthetic solar cells (DSPECs) to initiate the cleavage of C-C/C-O bonds in lignin and related model compounds. This approach takes advantage of

Biochar derived from lignocellulosic biomass has been used as a low-cost adsorbent in wastewater treatment applications. Due to its rich porous structure and good electrical conductivity, biochar can be used as a cost-effective electrode material for capacitive deionization of water. In this work, willow biochar was prepared through carbonization of shrub willow chips, activated with potassium hydroxide, and loaded with manganese dioxide (WBC-K-MnO2 nanocomposite). The prepared materials were used to electrochemically adsorb Pb2+ from aqueous solutions. Under the applied potential of 1.0 V, the WBC-K-MnO2 electrode exhibited a high Pb2+ specific electrosorption capacity (23.3 mg/g) as compared to raw willow biochar (4.0 mg/g) and activated willow biochar (9.2 mg/g). KOH activation followed by MnO2 loading on the surface of raw biochar enhanced its BET surface area (178.7 m2/g) and mesoporous volume ratio (42.1%). Moreover, the WBC-K-MnO2 nanocomposite exhibited the highest specific capacitance value of 234.3 F/g at a scan rate of 5 mV/s. The electrosorption isotherms and kinetic data were well explained by the Freundlich and pseudo-second order models, respectively. The WBC-K-MnO2 electrode demonstrated excellent reusability with a Pb2+ electrosorption efficiency of 76.3% after 15 cycles. Thus, the WBC-K-MnO2 nanocomposite can serve as a promising candidate for capacitive deionization of heavy metal contaminated water.

The photoelectrochemical production of fuels, exemplified by light-driven water splitting to hydrogen and oxygen, offers a sustainable option to offset dependence on fossil fuels. A low-cost, efficient, and stable photoelectrochemical approach to solar fuels remains elusive but using similar materials and photoelectrodes for chemical production or biomass conversion offers an appealing alternative. This work reports a facile method for fabricating pristine (undoped) BiVO

The seed-mediated method is a general procedure for the synthesis of gold nanorods (Au NRs), and reducing agents such as ascorbic acid (AA) and hydroquinone (HQ) are widely used for the growth process. Further, they are mild reducing agents; however, when AA is used, controlling the size of Au NRs with a higher aspect ratio (localized surface plasmon resonance (LSPR) peak, λLmax > 900 nm) is challenging because it results in a faster growth rate of Au NRs. In contrast, when HQ is used, Au NRs with a higher aspect ratio can be synthesized as it slows down the growth rate of the Au NRs and greatly enhanced the λLmax. However, the increase in λLmax is still needs not satisfactory due to the limited enhancement in the aspect ratio of Au NRs due to utilization of single reducing agent. The growth kinetics of the Au NRs can be modulated by controlling the reducing power of the reducing agents. In such scenario, judicious use of two reducing agents such as AA and HQ simultaneously can help us to design Au NRs of higher aspect ratio in a controlled manner due to the optimum growth rate resulting from the combined effect of both the reducing agents. In this study, we investigated the effect of the two reducing agents by controlling the volume ratios. When the growth solution contains both the reducing agents, the growth of Au NRs is first initiated by the fast reduction of Au3+ to Au+ due to stronger reducing power of the AA and when the AA in the growth solution is completely utilized, further growth of the Au NRs continues as a result of the HQ thereby resulting to high aspect ratio Au NRs. Consequently, the LSPR peak (λLmax > 1275 nm) can be tuned by controlling the volume ratios of the reducing agents.

For the decomposition process of lignin, there have been several processes reported. However, low selectivity of oxidative cleavage is one of prime issues because of reaction under harsh condition such as high temperature and high pressure. To overcome these problems, especially, dye-sensitized photo-electrochemical cells (HAT-DSPEC), which used photocatalyst (RuC) and homogeneous catalysts incorporated system was suggested. it represents conversion efficiencies over 90% under 24 h light illumination (AM 1.5G). However, metal complex sensitizer has disadvantages like low stability, high cost and low absorption coefficient. In this study, for highly stable HAT-DSPEC process, metal based sensitizer was replaced by organic dye(5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid, L1) which has high stability and molar absorption coefficient. For regenerating dye molecules and oxidating lignin model compounds(LMCs), bicyclic nitroxyl derivates, such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), and 9-azabicyclo[3,3,1]nonan-3-one-9-oxyl (Keto-ABNO) was used. In HAT-ODSPEC (organic dye-sesitized photo-electrochemical cell), Keto-ABNO exhibits higher photo-electrocatalytic activity than TEMPO for the oxidation and decomposition of LMC. The superior activity of L1 sensitizer with Keto-ABNO mediator is especially noteworthy of Caryl-Cα bond cleavage and with keto-ABNO exhibits 100% conversion yield of for 24hrs at room temperature while 86% with TEMPO. This HAT-ODSPEC process provides a unique foundation to perform selective C−C bond cleavage for real lignin conversion technologies.

Traditionally, Dye-sensitized photo electrochemical cells (DSPECs) have been targeted for solar-driven water splitting as production of fuels in aqueous media. Recently, hydrogen atom transfer incorporated dye-sensitized photo electrochemical cell (HAT-DSPEC) which used photocatalyst and homogeneous catalysts incorporating system was suggested for the decomposition process of lignin. This HAT-DSPEC system representing conversion efficiencies over 90% resulted in the formation of the oxidized ketone product from model compounds under simulated solar illumination with an applied bias 0.4 V vs Ag/Ag+ for 24 hrs. However, they have several issues such as long reaction time, low stability, and high bias potential. To overcome these problems, in this study, dye-sensitized photovoltaics’ advanced technic is applied. In HAT-DSPEC system, photo-anode (TiO2@Dye) has important role to produce oxoammonium species by oxidizing nitroxyl derivatives, such as 4-acetomido TEMPO (ACT). And these oxoammonium species act as a catalytic reaction with lignin model compounds (LMCs) to oxidizing of 1o or 2o alcohol and cleavage Caryl-Cα bond cleavage. However, in photo-anode, lots of charge recombination and electron back transfer occurs on the FTO and TiO2 surface and it induce low current and reactivity. For effectively producing oxoammonium species from photoelectrode, using blocking layer to passivate FTO surface from electrolytes and applying TiCl4 post-treatment for fast charge transport in TiO2 by enhancing interconnection of TiO2 nanoparticles. The photocurrent response of the m-TiO2@Ru470 photoelectrode in a nonaqueous electrolyte was examined with increasing mediator concentration during light on/off cycles under AM 1.5G illumination (100 mW/cm2), with an applied bias 0.1 V vs Ag/Ag+. Three kinds of electrode condition such as m-TiO2, BL/m-TiO2, BL/m-TiO2/TiCl4 post treatment was examined under same condition and treated photoelectrode (BL/m-TiO2/TiCl4) showed a significant increase in maximum photocurrent up to approximately 367.69 μA/cm2 with 3 mM ACT mediator, while BL/m-TiO2 exhibits 26.75 μA/cm2 and m-TiO2 1.26 μA/cm2. This result indicates that the blocking layer and TiCl4 post treatment enhanced electron lifetime and collection efficiency in the photoelectrode, as well as enhancing the capability of producing oxoammonium species.

Molecular-based dye-sensitized photoelectrochemical cells (DSPECs) have traditionally targeted solar-driven water splitting for the conversion of solar energy into fuels in aqueous media. Here we describe a novel approach to develop the DSPECs by combining hydrogen atom transfer mediator (HAT) with nanostructured semiconductors and photocatalysts for photocatalytic C−C/C−O bonds cleavage in lignin. This work reports the application of the DSPEC specifically designed to carry out photocatalytic oxidative cleavage of C−C/C−O σ-bonds in lignin model compounds at the photoanode. Current studies targeting the development of photocatalysts via HAT process for biomass conversion especially lignin depolymerization will be described, with the novel finding that a DSPEC utilizes a solar-driven catalytic conversion of woody biomass into value-added fuels and chemicals under aerobic mild conditions. The efficient photocatalytic bond cleavage in DSPECs is important to the development of sustainable approaches for lignin depolymerization and biomass conversion.

Traditionally, Dye-sensitized photo electrochemical cells (DSPECs) have been targeted for solar-driven water splitting as production of fuels in aqueous media. Recently, hydrogen atom transfer incorporated dye-sensitized photo electrochemical cell (HAT-DSPEC) which used photocatalyst and homogeneous catalysts incorporating system was suggested for the decomposition process of lignin. This HAT-DSPEC system representing conversion efficiencies over 90% resulted in the formation of the oxidized ketone product from model compounds under simulated solar illumination with an applied bias 0.4 V vs Ag/Ag+ for 24 hrs. However, they have several issues such as long reaction time, low stability and high bias potential. To overcome these problems, in this study, dye-sensitized photovoltaics’ advanced technic is applied. In HAT-DSPEC system, photo-anode (TiO2@Dye) has important role to produce oxoammonium species by oxidizing HAT mediator. And these oxidized HAT do a catalytic reaction with target materials: lignin model compounds (LMCs). However, in photo-anode, lots of charge recombination and electron back transfer occurs on the FTO and TiO2 surface. So, for effectively producing oxoammonium species from photoelectrode, using blocking layer to passivate FTO surface from electrolytes and applying TiCl4 post-treatment enhances charge transport in TiO2. The photocurrent response of the m-TiO2@Ru470 photoelectrode in a nonaqueous electrolyte was examined with increasing mediators concentration during light on/off cycles under AM 1.5G illumination (100 mW/cm−2), with an applied bias 0.4 V vs Ag/Ag+. Comparing three kinds of condition such as m-TiO2, BL/m-TiO2, BL/m-TiO2/TiCl4 post treatment, showed a significant increase in maximum photocurrent up to approximately 49.3, 101.3, 231.6 μA/cm−2 with 5 mM NHPI/2,6-Lutidine mediator. This result indicates that the blocking layer and TiCl4 post treatment enhanced electron life time and collection efficiency in the photoelectrode, as well as enhancing the capability of producing oxoammonium species.