Graphite Phase Carbon Nitride Research Articles

Synergistic enhancement of NC-GCN/Ag2O photocatalytic reduction of uranium by D-A and p-n junction structures

Recently, how to improve the photocatalytic uranium removal performance of Graphite-phase carbon nitride (GCN) has always been a hot research topic. In this paper, a new strategy based on p-n junction and D-A structure is proposed to improve the photocatalytic performance. And as a result, a novel cyano modified photocatalytic material NC-GCN/Ag2O was designed and prepared for the reduction of U(VI). Interestingly, the material shows better adsorption performance for U(VI) in the dark treatment stage, and its removal of U(VI) is close to 70 % under the initial U(VI) concentration of 20 ppm and the solid–liquid ratio of 0.2 g/L. And the adsorption is in accordance with the Langmuir model and Pseudo second order model. After 30 min of illumination, the removal rate of U(VI) can reach 93.2 %, significantly higher than that of GCN (13.6 %) and NC-GCN10(37.7 %). It’s worth mentioning that photocatalytic reduction dominated the adsorption-reduction process for U(VI) removal after light exposure. In addition, after four cycles, the removal of U(VI) from the composite material decreased by only 5 % with no change in the crystal structure, i.e., it has good reusability and stability. Meanwhile, there was no significant interference with other ions except for Cu2+ and V5+, which had a weak interference. Finally, a new mechanism for U(Ⅵ) reduction was proposed.

Defect-rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0 C) and satisfactory areal capacity (5.5 mAh cm−2 at 0.2 C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6% capacity retention after 100 cycles at 0.5 C) and outstanding rate performance (695 mAh/g at 2.0 C), and superior high loading performance (5.1 mAh cm−2 at 0.1 C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Spherical g-C3N4@PDA nanocarrier for synergistic chemo-photothermal tumor therapy

In this paper, by wrapping the near-infrared (NIR) response polydopamine (PDA) as a nanocoating on the surface of spherical nano graphitic phase carbon nitride (g-C3N4), a multifunctional g-C3N4/PDA (CNP) nanocarrier platform was prepared. The π-conjugation system in PDA and the electronegative hydroxyl groups on the surface of CNP promote the creation of abundant active sites, which had a high drug loading rate of about 98.5 % for the electropositive GA. Due to the strong NIR reaction of CNP, the release of GA from CNP/GA can be greatly accelerated by the rising temperature, bonding disruption and charge transfer. Moreover, the photo-generated electron-hole pairs could be excited by the NIR effect of CNP, which promotes the production of ROS (·OH, ·O2– and 1O2) to induce apoptosis in HepG2 cells. Thus, the present spherical CNP nanocarrier with a combination of enzyme-mimic activity and NIR-responsive properties has a great potential for chemo-photothermal synergistic tumor therapy.

Portable and Flexible Hydrogel Sensor for On-Site Atrazine Assay on Agricultural Products.

There is growing attention focused toward the problems of ecological sustainability and food safety raised from the abuse of herbicides, which underscores the need for the development of a portable and reliable sensor for simple, rapid, and user-friendly on-site analysis of herbicide residues. Herein, a novel multifunctional hydrogel composite is explored to serve as a portable and flexible sensor for the facile and efficient analysis of atrazine (ATZ) residues. The hydrogel electrode is fabricated by doping graphite-phase carbon nitride (g-C3N4) into the aramid nanofiber reinforced poly(vinyl alcohol) hydrogel via a simple solution-casting procedure. Benefiting from the excellent electroactivity and large specific surface area of the solid nanoscale component, the prepared hydrogel sensor is capable of simple, rapid, and sensitive detection of ATZ with a detection limit down to 0.002 ng/mL and per test time less than 1 min. After combination with a smartphone-controlled portable electrochemical analyzer, the flexible sensor exhibited satisfactory analytical performance for the ATZ assay. We further demonstrated the applications of the sensor in the evaluation of the ATZ residues in real water and soil samples as well as the user-friendly on-site point-of-need detection of ATZ residues on various agricultural products. We envision that this flexible and portable sensor will open a new avenue on the development of next-generation analytical tools for herbicide monitoring in the environment and agricultural products.

Photothermal graphite phase carbon nitride membrane intercalated with polyoxovanadate for efficient solar steam generation

Graphite phase carbon nitride (GCN) has shown promising prospects in diverse fields due to its exfoliating two-dimensional (2D) layered structure, adjustable electronic properties, wide absorption of visible light, and excellent chemical stability. It is crucial to accurately regulate and functionalize the intercalation space of 2D membrane materials for specific functions. Herein, we demonstrate the first GCN-based photothermal membrane for efficient solar steam generation. The polyoxovanadate anion was intercalated in between protonated GCN layers via an electrostatic interaction strategy, which enlarged the layer spacing up to ∼12.4 Å and increased the water and salt ions transport capability. Owing to the excellent photothermal conversion efficiency of polyoxovanadate, the polyoxovanadate-intercalated GCN membrane fabricated by suction filtration exhibited effective absorbance in full solar spectrum (>95.5 %) and achieved efficient solar steam generation (2.62 kg m−2 h−1 under 1 sun) when floating on water. The long-term durability test showed that the evaporation performance is stable and no salt precipitation observed. These findings not only expand the functional applications of carbon nitride materials, but also provide a new strategy for solar desalination.

Preparation of High-Efficiency Fe/N-Doped Carbon Catalysts Derived from Graphite Phase Carbon Nitride for Reduction of Oxygen

Preparation of High-Efficiency Fe/N-Doped Carbon Catalysts Derived from Graphite Phase Carbon Nitride for Reduction of Oxygen

Efficient photocatalytic hydrogen peroxide production over S-scheme In2S3/molten salt modified C3N5 heterojunction

Graphitic phase carbon nitride (g-C3N5), as a novel n-type metal-free material, is employed as a visible light-receptive catalyst because of its narrow band gap and abundant nitrogen. To overcome the low carrier mobility efficiency of g-C3N5, its modification by K ions was adopted. In addition, In2S3 was selected to couple with modified g-C3N5 to overcome the recombination of photogenerated e−/h+. As a novel photocatalytic material, it was proven to possess a high visible light absorption capacity and a strong H2O2 production ability (up to 3.89 mmol⋅L-1 in 2 h). Moreover, a S-scheme heterojunction structure was successfully constructed between the two materials, which was tested and confirmed to be successful in raising the photogenerated e−/h+ separation efficiency. Ultimately, the primary processes of photocatalytic H2O2 production were summarized by superoxide radical and rotating disc electron measurements. This research provides a fresh perspective for the synthesis of C3N5-based S-scheme heterojunction photocatalysts for producing H2O2.

Bi, K co-doped graphitic phase carbon nitride for efficient photocatalytic H2O2 production

The emerging photocatalytic production of hydrogen peroxide (H2O2) using graphitic carbon nitride (g-C3N4) has attracted a lot of attention for its potential applications in various fields. However, However, the catalytic activity of pure g-C3N4 is still limited. Herein, Bi, K co-doped g-C3N4 (BixKy-CN) was prepared by co-thermal polymerization of a mixture of potassium nitrate, bismuth nitrate, melamine, and urea. The obtained Bi3.6K3-CN composite possesses more negative conduction and valence band positions that can, to some extent, enhance photocatalytic performance by lowering the energy barrier of redox reactions and by enhancing electron absorption capacity. Additionally, the pyrolysis process of the potassium nitrate and bismuth nitrate has a considerable impact on the formation of the morphology of g-C3N4, generating a porous lamellar-structure with nitrogen defects, resulting in increased oxygen adsorption and utilization capacity. These synergistic effects enable Bi3.6K3-CN to exhibit excellent photocatalytic activity and cycling stability for H2O2 production. After 3 hours of visible light irradiation, the production of H2O2 catalyzed by Bi3.6K3-CN can reach 1207.72 μmol L-1, which is 57 times higher than that of pure g-C3N4.

Z-scheme heterojunction composed of Fe-doped g-C3N4 and Bi2MoO6 for photo-fenton degradation of antibiotics over a wide pH range: Activity and toxicity assessment

In photo-Fenton technology, the narrower pH range limits its practical application for antibiotic wastewater remediation. Therefore, in this study, a Z-scheme heterojunction photo-Fenton catalyst was constructed by Fe-doped graphite-phase carbon nitride in combination with bismuth molybdate for the degradation of typical antibiotics. Fe doping can shorten the band gap and increase visible-light absorption. Simultaneously, the constructed Z-scheme heterojunction provides a better charge transfer pathway for the photo-Fenton reaction. Within 30 min, Fe3CN/BMO-3 removed 95.54% of tetracycline hydrochloride (TC), and its remarkable performance was the higher Fe3+/Fe2+ conversion efficiency through the decomposition of H2O2. The Fe3CN/BMO-3 catalyst showed remarkable photo-Fenton degradation performance in a wide pH range (3.0–11.0), and it also had good stability in the treatment of TC wastewater. Furthermore, the order of action of the active species was h+ > ·O2− >1O2 > ·OH, and the toxicity assessment suggested that Fe3CN/BMO-3 was effective in reducing the biotoxicity of TC. The catalyst proved to be an economically feasible and applicable material for antibiotic photo-Fenton degradation, and this study provides another perspective on the application of elemental doping and constructed heterojunction photo-Fenton technology for antibiotic water environmental remediation.

Integration of WOx/1D C3N4/2D C3N4 multi-junction through in-situ “PTA-Mel” ionic microenvironment for efficient aromatic wastes degradation via charge carrier separation improvement

High photogenerated carrier recombination inhibits the widespread application of graphite-phase carbon nitride (g-C3N4). Construction of junctions is an effective strategy but still under challenges, such as tedious procedure and limited efficiency. Herein, WOx/1D g-C3N4/2D g-C3N4 multi-junction with enhanced separation of photogenerated carriers was one-pot integrated through in-situ “PTA-Mel” ionic microenvironment by mixing phosphotungstic acid (PTA) and melamine (Mel). Protonated Mel by PTA contributed to the formation of 1D g-C3N4 and the decomposition of [P(W3O40)4]3- produced WOx. 1D g-C3N4 and WOx with oxygen-vacancy deficient provided channels and caves for photoelectrons transfer, respectively. Compared with pure g-C3N4, the degradation rate constants of Rh B and tetracycline hydrochloride (TC) by WOx/1D g-C3N4/2D g-C3N4 are 2.34 and 1.45 times high respectively due to the excellent visible light absorption and improved photogenerated carrier separation. This method could be extended to the design of multiple heterojunctions in one photocatalyst through a facile process.

Dual elemental doping activated signaling pathway of angiogenesis and defective heterojunction engineering for effective therapy of MRSA-infected wounds

Multi-drug resistant bacterial infections pose a significant threat to human health. Thus, the development of effective bactericidal strategies is a pressing concern. In this study, a ternary heterostructure (Zn–CN/P-GO/BiS) comprised of Zn-doped graphite phase carbon nitride (g-C3N4), phosphorous-doped graphene oxide (GO) and bismuth sulphide (Bi2S3) is constructed for efficiently treating methicillin-resistant Staphylococcus aureus (MRSA)-infected wound. Zn doping-induced defect sites in g-C3N4 results in a reduced band gap (ΔE) and a smaller energy gap (ΔEST) between the singlet state S1 and triplet state T1, which favours two-photon excitation and accelerates electron transfer. Furthermore, the formation of an internal electric field at the ternary heterogeneous interface optimizes the charge transfer pathway, inhibits the recombination of electron-hole pairs, improves the photodynamic effect of g-C3N4, and enhances its catalytic performance. Therefore, the Zn–CN/P-GO/BiS significantly augments the production of reactive oxygen species and heat under 808 nm NIR (0.67 W cm−2) irradiation, leading to the elimination of 99.60% ± 0.07% MRSA within 20 min. Additionally, the release of essential trace elements (Zn and P) promotes wound healing by activating hypoxia-inducible factor-1 (HIF-1) and peroxisome proliferator-activated receptors (PPAR) signaling pathways. This work provides unique insight into the rapid antibacterial applications of trace element doping and two-photon excitation.

Embedded iron and nitrogen co-doped carbon quantum dots within g-C3N4 as an exceptional PMS photocatalytic activator for sulfamethoxazole degradation: The key role of Fe[sbnd]N bridge

The covalent modification of graphite-phase carbon nitride (g-C3N4) by carbon quantum dots (CQDs) is a promising way to improve its photocatalytic performance. Although CQDs can act as charge mediator for electrons storage and transfer, it is crucial to construct efficient interfaces, which serves as active sites for tight connect with g-C3N4 and fast release of electrons. Herein, a novel iron and nitrogen co-doped carbon quantum dots (Fe, N-CQDs) assembled g-C3N4 composite (FNCCN) was constructed via FeN bridge by hydrothermal and thermal polymerization methods. The FNCNN rivaled popular nitrogen-doped carbon quantum dots (N-CQDs) combined with g-C3N4 composites for peroxymonosulfate (PMS) activation and degradation of sulfamethoxazole (SMX). The SMX degradation rate (0.0963 min−1) is 5.38 and 3.15 times higher than that of g-C3N4 and N-CQDs/g-C3N4. The characterization and DFT calculation results suggest that Fe, N-CQDs was successfully incorporated into carbon matrix of g-C3N4 via FeN covalent bond, which joints the two counterparts closely and creates electron transport channels for higher electrons transfer efficiency. The FeN coordinated structure promotes PMS reduction on Fe2+ of FeN sites for HO and SO4- production and expedited photo carries separation through Fe3+/Fe2+ cycling. In addition, the degradation efficiency, ROS identification, EPR test and degradation pathway of SMX was determined, and the intermediate toxicity of degradation products was predicted. This work constructed a tight atomic-level connection between hydrophobic g-C3N4 and hydrophilic CQDs, which improved an effective strategy for accelerating electron transport and efficient photocatalytic activation of PMS.

One-Step Synthesis of Alkali Metal-Hydroxyl Double Modified Graphite Phase Carbon Nitride and Photocatalytic Degradation of Phenolic Compounds

In this work, potassium ion-hydroxyl double modified graphite phase carbon nitride (KCN–OH) was synthesized in one step by alkali hydrothermal (AH) method. The as-prepared catalysts were characterized by XRD, FT-IR, UV–Vis, N2 adsorption, SEM, XPS, PL, ESR, TPD and EIS. The introduction of potassium ion causes the reduced crystal size, increased specific surface area and promoted electron–hole separation efficiency of as-prepared catalyst. The hydroxyl group not only further improves the electron–hole separation efficiency but, as the electron donor group, can also make stronger interaction between catalyst and acidic phenolic compounds. The photocatalytic degradation of phenol was investigated under visible light. The results show that the phenol degradation rate constant of KCN–OH is 0.22 h[Formula: see text] under visible light, which is over 3.7 and 2.0 times higher than that of neat g-C3N4 and single hydroxyl-modified g-C3N4. KCN–OH also displays outstanding catalytic and structural stability. The possible reaction mechanism is discussed in this paper.

Utilising bauxite residue (red mud) to construct Z-type heterojunction for formaldehyde degradation

The photocatalytic treatment of pollutants has garnered significant attention owing to its ability to safely and efficiently treat pollutants without secondary contamination. However, the complexity of synthesis methods and the high costs of photocatalysts remain major challenges for the industrial application of this technology. The high content of α-Fe2O3 metal semiconductors in red mud (RM) presents an opportunity for the effective preparation of RM-based α-Fe2O3 composites for catalytic degradation. Graphitic-phase carbon nitride features a similar energy band structure to α-Fe2O3 and demonstrates excellent photocatalytic properties. Herein, we directly prepared a novel Z-scheme-heterojunction g-C3N4/RM composites via a one-step calcination method by reconstructing the interface between RM and melamine. Comprehensive characterisations revealed the formation of a Z-scheme heterojunction between g-C3N4 and α-Fe2O3. This significantly improved the spatial separation of photogenerated carriers, enabling the efficient degradation of formaldehyde. The degradation efficiency reached 63.04% after 2 h of light exposure, and the composites exhibited excellent recyclability. The optical adsorption and photocatalytic properties of this newly developed composite material were significantly enhanced compared with pristine RM, which degraded 26.96% of formaldehyde under similar conditions. This study marks the first application of Z-type heterojunctions constructed from bauxite residue and nonmetallic semiconductors for degrading formaldehyde, an air pollutant. Our work offers new insights into leveraging solid wastes for high-value-added advanced catalytic applications.

Unmasking the Electrochemiluminescence Properties of Ternary Mn/Fe/Co Metals Doped Porous g-C3N4 Fiber-like Nanostructure.

Graphitic-phase carbon nitride (g-C3N4) materials have exhibited increasingly remarkable performance as emerging electrochemiluminescence (ECL) emitters, owing to their unique optical and electronic properties; however, the ECL merits of porous g-C3N4 nanofibers doped with ternary metals are not yet explored. Deciphering the ECL properties of trimetal-doped g-C3N4 nanofibers could provide an exquisite pathway for ultrasensitive sensing and imaging with impressive advantages of minimal background signal, great sensitivity, and durability. Herein, we rationally synthesized g-C3N4 nanofibers doped atomically with Mn, Fe, and Co elements (Mn/Fe/Co/g-C3N4) in a one-pot via the protonation in ethanol and annealing process driven by the rolling up mechanism. The ECL performance of g-C3N4 with and without metal dopants was investigated and compared with standard Ru(bpy)32+ in the presence of potassium persulfate (K2S2O8) as the coreactant. Notably, g-C3N4 nanofibers doped with metal ions exhibited an ECL efficiency of 483% that was 4.83 times higher than that of Ru(bpy)32+. Mechanistic investigations unveiled that the g-C3N4 nanofibers possess a large surface area and, as a result, exhibit a reduced interfacial impedance within the porous microstructure. These factors contribute to the acceleration of charge transfer rates and the stabilization of charge carriers and excitons, ultimately facilitating the ECL process. This research endeavor may pave the way for a new hot research area and serves as a powerful tool for elucidating fundamental inquiries of ECL on one-dimensional g-C3N4 nanostructures.

Photocatalytic degradation of ciprofloxacin by Gd-Co/g-C3N4 under low-power light source: Degradation pathways and mechanistic insights

Ciprofloxacin hydrochloride (CIP) is remained in the natural environment. Photocatalysis is a promising technology for removing hard-to-degrade pollutants from water. For this purpose, we constructed a three-dimensional porous structure of graphitic-phase carbon nitride (3D g-C3N4) and doped rare earth element Gd and metal Co into 3D g-C3N4 to form a photocatalyst (Gd-Co/CN). We conducted photocatalytic experiments to evaluate its photocatalytic activity with CIP as the target pollutant. Experimental results showed that Gd-Co/CN had the best photocatalytic degradation of CIP under a 30 W LED lamp. The increase in photocatalytic activity is mainly attributed to the doping of Gd and Co expanding the specific surface area of 3D g-C3N4, and providing more reaction sites for photocatalytic reactions. Gd-Co/CN enhances O2 adsorption and activation and generates radicals (O2− and h+), allowing efficient degradation of CIP under low-power light sources. Furthermore, Gd-Co/CN also showed excellent stability and reusability in cycling experiments. This study explored the degradation pathways and mechanisms of CIP by using ultra-high-performance liquid chromatography and mass spectrometry (HPLC-MS) and density functional theory (DFT). It provides a more energy-efficient and environmentally friendly method for the treatment of antibiotic wastewater.

Progress in Promising Semiconductor Materials for Efficient Photoelectrocatalytic Hydrogen Production.

Photoelectrocatalytic (PEC) water decomposition provides a promising method for converting solar energy into green hydrogen energy. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. However, the fairly low PEC efficiency of water decomposition by a semiconductor photoelectrode and photocorrosion seriously restrict the practical application of photoelectrochemistry. In this review, the mechanisms of PEC water decomposition are first introduced to provide a solid understanding of the PEC process and ensure that this review is accessible to a wide range of readers. Afterwards, notable achievements to date are outlined, and unique approaches involving promising semiconductor materials for efficient PEC hydrogen production, including metal oxide, sulfide, and graphite-phase carbon nitride, are described. Finally, four strategies which can effectively improve the hydrogen production rate-morphological control, doping, heterojunction, and surface modification-are discussed.

Multifunctional nanocomposites based on graphite-phase carbon nitride quantum dot-silver nanospheres for combined photothermal–photodynamic anti-tumor therapy

In this study, a g-CNQDs@AgNSs nanocomposite was successfully prepared based on graphite-phase carbon nitride quantum dots and silver nanospheres. Both in vitro and cellular experiments proved that the nanocomposite had good PTT/PDT effects, promising efficient combination therapy of tumors.

Neuron specific enolase assay based on the perovskite CoSn(OH)6 for enhancing the anodic electrochemiluminescence of luminol

Electrochemiluminescence (ECL) is a widely applied technique for trace detection and analysis, but the stability of luminophores and external environmental factors strongly influence the analysis results. Herein, a low-potential ECL sensing platform based on enhanced nanomaterial catalysis for the traditional system luminol-H2O2 is proposed for the detection of neuron specific enolase (NSE). In this strategy, Au nanoparticles modified with three-dimensional graphitic phase carbon nitride (3DCNA) were used as a solid platform for antibodies (Ab2), which not only solved the problem of accumulation between traditional two-dimensional nanosheets but also had good biocompatibility, ensuring the accuracy of the analysis results. CoSn(OH)6, benefiting from its inherently higher catalytic activity and greater number of adsorption sites on perovskite hydroxide, can catalyze the oxidationreduction reaction of H2O2 to improve the ECL behavior of luminol and lower the applied voltage to reduce damage to biological activity. Owing to these exceptional properties, this proposed sandwich ECL immunosensor was explored for the primary diagnosis of SCLC by detecting NSE with a detection limit of 0.18 pg mL–1. It exhibited satisfactory linearity in the range of 0.0005 ng mL–1 to 100 ng mL–1 with favorable stability, excellent specificity, and good reproducibility. This study provides an important reference for low-potential ECL with promising application prospects in actual clinical analysis and detection.

Nickel-decorated graphite phase carbon nitride photocatalysts coupled with carbazole-based calixarene dyes for high-efficiency visible light-driven hydrogen evolution

The development of artificial devices that mimic the highly efficient and sophisticated photosystems found in nature is a subject worthy of in-depth study. Two calixarene D-π-A dyes, C4-CZSTP and C4-CZBTP, containing an N-methylcarbazole group as a secondary auxiliary electron donor, are synthesized on the basis of our previously reported calixarene dye C4-BTP. These dyes are then cooperated with Ni-deposited g-C3N4 to prepare ternary photocatalysts, denoted as C4-CZSTP/Ni/g-C3N4, C4-CZBTP/Ni/g-C3N4 and C4-BTP/Ni/g-C3N4, and their photocatalytic performances are evaluated under visible light irradiation. The optimized 4.0 wt% C4-CZSTP/Ni/g-C3N4 sample gives a remarkable H2 evolution rate of 5552 μmol g−1 h−1, representing one of the highest records among the reported analogous systems based on g-C3N4. And after an extended test of 49 h, a total H2 yield of 63.57 mmol g−1 is obtained, corresponding to a turnover number (TON) based on C4-CZSTP moles (TONC4-CZSTP) of 3180. This performance can be attributed to the enhanced light-harvesting and photoelectron conversion of the as-prepared calixarene dyes, the adjusted energy levels and the effective cooperation of the three components. The optimal performance of C4-CZSTP/Ni/g-C3N4 among the three dye-sensitized systems is due to its higher lowest unoccupied molecular orbital (LUMO) value, i.e. stronger electronic driving force from the excited dye to g-C3N4. This study provides an interesting example for the design and preparation of a low-cost, high-efficiency and noble metal-free photocatalytic system for solar fuel production.