Mesoporous ferriferrous oxide nanoreactors modified on graphitic carbon nitride towards improvement of physical, photoelectrochemical properties and photocatalytic performance

NCQDs active sites as effective collectors of charge carriers towards enhanced photocatalytic activity of porous Co3O4

In this work, different proportions of N-doped carbon quantum dots/porous Co3O4 (NCQDs/p-Co3O4) NCQDs/Co3O4 composite photocatalysts were prepared by a simple self-assembly method. It was demonstrated by a series of characterizations that 50% NCQDs/Co3O4 has a good visible light response and low electrochemical impedance. The photocatalytic degradation of TC was investigated by the 50% NCQDs/p-Co3O4 composite photocatalyst, and the results showed that the degradation effect of TC reached 81.2% within 120 min. The higher photocatalytic activity of 50% NCQDs/p-Co3O4 was analyzed probably because NCQDs can improve the separation efficiency of photogenerated electron-hole pairs and p-Co3O4 can provide a larger specific surface area and thus has more active sites. This study provides a new strategy for improving the photodegradation activity of Co3O4 photocatalysts.

A novel immobilized horseradish peroxidase platform driven by visible light for the complete mineralization of sulfadiazine in water

A novel immobilized enzyme driven by visible light was prepared and used for complete mineralization of antibiotics in water bodies. The immobilized enzyme was composed of carbon nitride modified by biochar (C/CN) and horseradish peroxidase (HRP), establishing the photo-enzyme coupling system with synergistic effect. Among them, the introduction of biochar not only improves the stability and loading capacity of the enzyme, but also improves the light absorption capacity and carrier separation efficiency of the photocatalyst. After the optimization of immobilization process, the solid load of HRP could reach 251.03 mg/g, and 85.03 % enzyme activity was retained after 18 days of storage at 4 °C. In the sulfadiazine (SDZ) degradation experiment, the degradation rate of HRP/C3/CN reached 71.21 % within 60 min, which was much higher than that of HRP (2.33 %), CN (49.78 %) and C3/CN (58.85 %). In addition, under the degradation of HRP/C/CN, the total organic carbon (TOC) removal rate of SDZ reached 53.14 %, which was 6.47 and 1.74 times that of CN and C3/CN, respectively. This study shows that the introduction of biochar is of great significance to the photo-enzyme cascade coupling system and provides a new strategy for the application of HRP&g-C3N4 system in wastewater treatment.

Influences of different carbon substrates on the morphologies of carbon/g-C3N4 photocatalytic composites and the purification capacities of different composites in the weak UV underwater environment

In order to explore the influence of various carbon introduction on the morphology and photodegradation performance of C/g-C₃N₄ composites, three kinds of different carbon materials: carbon nanotubes (CNT), graphene (GN) and carbon fibers (CF) were introduced to modify g-C₃N₄, and the morphologies, light absorption capacities and the underwater purifications of the composite photocatalysts were investigated. Results showed that the composites synthesized with different carbon substrates shows great differences in growth morphology. In addition, the introduction of various carbon sources also has a great impact on the physical and chemical properties of the composites. Compared with GN/g-C₃N₄ and CF/g-C₃N₄, CNT/g-C₃N₄ shows strong light absorption ability, especially in long-wavelength region (570-660 nm). To further study the difference of degradation ability of the composites in the underwater environment, the purification performance of modified g-C₃N₄ at different water depths were carried out. The results show that under 40 cm of water, where the light intensity and ultra violet spectral are seriously attenuated, the purification efficiency of CNT/g-C₃N₄ at 40 cm is 3.35 times than that of g-C₃N₄. This work provides insight in the design of highly efficient metal-free photocatalysts for the environmental remediation.

Dual-Mode-Driven Micromotor Based on Foam-like Carbon Nitride and Fe3O4 with Improved Manipulation and Photocatalytic Performance

Micro/nanomotors have emerged as a vibrant research topic in biomedical and environmental fields due to their attractive self-propulsion as well as small-scale functionalities. However, single actuated micro/nanomotors are not adaptive in facing intricate natural and industrial environments. Herein, we propose a new dual-mode-driven micromotor based on foam-like carbon nitride (f-C₃N₄) with precipitated Fe₃O₄ nanoparticles, namely, Fe₃O₄/f-C₃N₄, powered by chemical/magnetic stimuli for rapid reduction of organic pollutants. The Fe₃O₄/f-C₃N₄ motor composed of a three-dimensional (3D) porous "foam-like" structure and precipitated Fe₃O₄ nanoparticles (ca. 50 nm) not only exhibits efficient photocatalytic performance under visible light but also shows versatile and programmable motion behavior under the control of external magnetic fields. The aggregation of the micromotor under an external rotating magnetic field further enhances the catalytic activity by the increased local catalyst concentration. Furthermore, the magnetic property endows the micromotor with easy recyclability. This study provides a novel dual-mode-driven micromotor for antibiotics removal with magnetic field and light-enhanced performance in industrial wastewater treatment at a low cost.

Cu/PCN Metal-Semiconductor Heterojunction by Thermal Reduction for Photoreaction of CO2-Aerated H2O to CH3OH and C2H5OH

g-C₃N₄-based materials show potential for photoreduction of CO₂ to oxygenates but are subjected to fast recombination of photogenerated charge carriers. Here, a novel Cu-dispersive protonated g-C₃N₄ (PCN) metal-semiconductor (m-s) heterojunction from thermal reduction of a Cu₂O/PCN precursor was prepared and characterized using in situ X-ray diffraction, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible (UV-vis) spectra, photoluminescence (PL) spectra, transient photocurrent response, and electrochemical impedance spectroscopy (EIS). The Cu amount in Cu/PCN and the reduction temperature affected the generation of CH₃OH and C₂H₅OH from the photoreaction of CO₂-aerated H₂O. During calcination of Cu₂O/PCN in N₂ at 550 °C, Cu₂O was completely reduced to Cu with even dispersion, and a m-s heterojunction was obtained. With thermal exfoliation, Cu/PCN showed a specific surface area and layer spacing larger than those of PCN. Cu/PCN-0.5 (12.8 wt % Cu) exhibited a total carbon yield of 25.0 μmol·g^-1 under UV-vis irradiation for 4 h, higher than that of Cu₂O/PCN (13.6 μmol·g^-1) and PCN (6.0 μmol·g^-1). The selectivity for CH₃OH and C₂H₅OH was 51.42 and 46.14%, respectively. The PL spectra, transient photocurrent response, and EIS characterizations indicated that Cu/PCN heterojunction promotes the separation of electrons and holes and suppresses their recombination. The calculated conduction band position was more negative, which is conducive to the multielectron reactions for CH₃OH and C₂H₅OH generation.

Nickel supported on Nitrogen-doped biomass carbon fiber fabricated via in-situ template technology for pH-universal electrocatalytic hydrogen evolution

Developing alternatives to noble metal electrocatalysts for hydrogen production via water splitting is a challenging task. Herein, a novel electrocatalyst with Ni nanoparticles disperesed on N-doped biomass carbon fibers (NBCFs) was prepared through a simple in-situ growth process using Ni-ethanediamine complex (NiC) as the structure-directing agent. The in-situ template effect of the NiC facilitated the formation of Ni-N bonds between the Ni nanoparticles and NBCFs, which not only prevented the aggregation and corrosion of the Ni nanoparticles, but also accelerated the electron transfer in the electrochemical reaction, thus improving the hydrogen evolution reaction (HER) activity of the electrocatalyst. As expected, the optimal Ni/NBCF-1-H₂ electrocatalyst exhibited better HER activity over the entire pH range than the control Ni/NBCF-1-N₂ and Ni/NBCF-1-NaBH₄ samples. The HER overpotentials of the Ni/NBCF-1-H₂ electrocatalyst were as low as 47, 56, and 100 mV in alkaline (pH = 13.8), acidic (pH = 0.3), and neutral (pH = 7.3) electrolytes, respectively at the current density of 10 mA cm^-2. Meanwhile, the Ni/NBCF-1-H₂ sample could run continuously for 100 h, exhibiting outstanding stability. This work provides a feasible method for developing efficient and cheap electrocatalysts derived from biomass carbon materials using the in-situ template technology.

Promoting Spatial Charge Transfer of ZrO2 Nanoparticles: Embedded on Layered MoS2/g-C3N4 Nanocomposites for Visible-Light-Induced Photocatalytic Removal of Tetracycline

Photocatalytic degradation is a sustainable technique for reducing the environmental hazards created by the overuse of antibiotics in the food and pharmaceutical industries. Herein, a layer of MoS2/g-C3N4 nanocomposite is introduced to zirconium oxide (ZrO2) nanoparticles to form a "particle-embedded-layered" structure. Thus, a narrow band gap (2.8 eV) starts developing, deliberated as a core photodegradation component. Under optimization, a high photocatalytic activity of 20 mg/L TC at pH 3 with ZrO2@MoS2/g-C3N4 nanocomposite was achieved with 94.8% photocatalytic degradation in 90 min. A photocatalytic degradation rate constant of 0.0230 min-1 is determined, which is 2.3 times greater than the rate constant for bare ZrO2 NPs. The superior photocatalytic activity of ZrO2@MoS2/g-C3N4 is due to the dual charge-transfer channel between the MoS2/g-C3N4 and ZrO2 nanoparticles, which promotes the formation of photogenerated e-/h+ pairs. Charge recombination produces many free electron-hole pairs, which aid photocatalyst reactions by producing superoxide and hydroxyl radicals via electron-hole pair generation. The possible mechanistic routes for TC were investigated in-depth, as pointed out by the liquid chromatography-mass spectrometry (LC-MS) investigation. Overall, this work shows that photocatalysis is a feasible sorbent approach for environmental antibiotic wastewater treatment.

pH-induced hydrothermal synthesis of Bi2WO6 nanoplates with controlled crystal facets for switching bifunctional photocatalytic water oxidation/reduction activity

Bifunctional photocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have attracted growing interest to understand the mechanisms governing different evolution reactions, and the bifunctional activity of a single type of crystalline photocatalyst has gained especial attention. We herein report the high photocatalytic OER and HER activities of Bi₂WO₆ nanoplates (BWO NPs) which are synthesized by a simple hydrothermal method, and the switchable OER and HER performances controlled by the pH value of the precursor solvent. In the pH range from 4 to 9, the thickness of BWO NPs along the [001] direction exhibits interesting dependence on the pH value, which decreases as the pH value increases. Correspondingly, the BWO NPs obtained at the pH value of 7 (BWO-7) show the highest photocatalytic OER activity, while the BWO NPs synthesized at the pH value of 9 (BWO-9) exhibit the highest photoactivity towards HER. The electronic band structure analysis indicates that the highest photocatalytic OER activity is related to the band alignment of the valence band maximum of Bi₂WO₆, which determines the efficient separation of photogenerated electrons and holes as well as the fast charge transfer kinetics. The crystal facet evolution resulting from thickness reduction promotes the exposure of {001} facets for HER and decreases the exposure of {100} and {010} facets for OER. This work provides new insights into the combined effects of crystal facets and electronic band structures on photocatalysis.

Fabrication of graphitic carbon nitride functionalized P-CoFe2O4 for the removal of tetracycline under visible light: Optimization, degradation pathways and mechanism evaluation

In this study, nano-sized CoFe₂O₄ composites were prepared through co-precipitation process. Then the phosphorus-doped strong magnetic graphitic carbon nitride hybrids composites (P-CoFe₂O₄@GCN) was stemmed from the CoFe₂O₄ composites via the thermal polymerization method. The TEM results show that the CoFe₂O₄ nanoparticles have been successfully embedded into the graphitic carbon nitride (GCN). The BET specific surface area of P-CoFe₂O₄@GCN-1 could reach 36.91 m²/g, which was 5.38 times higher than that of GCN. Thus, it provided sufficient reaction active sites to enhance the photocatalytic activity for tetracycline (TC) decomposition. The results from the photocatalytic experiments showed that the degradation efficiency of TC by P-CoFe₂O₄@GCN-1 could reach 96.2% within 60 min, which is 3.19 times higher than that of GCN. The h⁺, O₂•^- and •OH radicals detected by the electron spin resonance (ESR) were responsible for the TC decomposition in the photocatalytic reaction system. Persulfate (PS) can further activate the hybrid mixture system, and the fitting model predicted by the response surface methodology (RSM) indicated that the maximum tetracycline removal could reach 99.6% within 30 min. In addition, the degradation intermediates of TC were detected by HPLC-MS and the photodegradation mechanism was discussed.

Diluted-CdS Quantum Dot-Assisted SnO2 Electron Transport Layer with Excellent Conductivity and Suitable Band Alignment for High-Performance Planar Perovskite Solar Cells

An electron transport layer (ETL) with excellent conductivity and suitable band alignment plays a key role in accelerating charge extraction and transfer for achieving highly efficient planar perovskite solar cells (PSCs). Herein, a novel diluted-cadmium sulfide quantum dot (CdS QD)-assisted SnO₂ ETL has been developed with a low-temperature fabrication process. The slight addition of CdS QDs first enhances the crystallinity and flatness of SnO₂ ETLs so that it provides a promising workstation to obtain high-quality perovskite absorption layers. It also amazingly increases the conductivity of the SnO₂ ETL by an order of magnitude and regulates the energy level matching between the SnO₂ ETL and perovskite. These outstanding properties greatly accelerate the charge extraction and transfer. Thus, the MAPbI₃-based PSCs with such a diluted-CdSQD-assisted SnO₂ ETL achieve a maximum power conversion efficiency of 20.78% and obtain a better stability of devices in air. These findings testify the importance and potential of semiconductor QD modification on ETLs, which may pave the way for developing such composite ETLs for further enhancing photovoltaic performance of planar PSCs.

Copper iodide decorated graphitic carbon nitride sheets with enhanced visible-light response for photocatalytic organic pollutant removal and antibacterial activities

The photocatalytic process is an environmentally-friendly procedure that has been well known in the destruction of organic pollutants in water. The multiple semiconductor heterojunctions are broadly applied to enhance the photocatalytic performances in comparison to the single semiconductor. Polymeric semiconductors have received much attention as inspiring candidates owing to their adjustable optical absorption features and simply adaptable electronic structure. The shortcomings of the current photocatalytic system, which restricts their technical applications incorporate fast charge recombination, low-utilization of visible radiation, and low immigration capability of the photo-induced electron-hole. This paper indicates the novel fabrication of new CuI/g-C₃N₄ nanocomposite by hydrothermal and ultrasound-assisted co-precipitation methods. The structure, shape, and purity of the products were affected by different weight percentages and fabrication processes. Electron microscope unveils that CuI nanoparticles are distributed on g-C₃N₄. The bandgap of pure carbon nitride is estimated at 2.70 eV, and the bandgap of the nanocomposite has increased to 2.8 eV via expanding the amount of CuI. The CuI/C₃N₄ nanocomposite has a great potential to degrade cationic and anionic dyes in high value because of its appropriate bandgap. It can be a great catalyst for water purification. The photocatalytic efficiency is affected by multiple factors such as types of dyes, fabrication methods, the light sources, mass ratios, and scavengers. The fabricated CuI/C₃N₄ nanocomposite exposes higher photocatalytic performance than the pure C₃N₄ and CuI. The photocatalytic efficiency of nanocomposite is enhanced by enhancing the amount of CuI. Besides, the fabricated CuI/C₃N₄ revealed remarkable reusability without the obvious loss of photocatalytic activity. The antibacterial activity of the specimens reveals that the highest antimicrobial activities are revealed against P. aeruginosa and E. coli. These results prove that the nanocomposite possesses high potential for killing bacteria, and it can be nominated as a suitable agent against bacteria.

High crystallinity and conjugation promote the polarization degree in O-doped g-C3N4 for removing organic pollutants

High crystallinity and extended conjugated system improve the polarization of O-doped g-C₃N₄, which efficiently promotes carrier separation.

A Z-scheme heterostructure constructed from ZnS nanospheres and Ni(OH)2 nanosheets to enhance the photocatalytic hydrogen evolution

ZnS and Ni(OH)₂ form a Z-scheme heterostructure, and the synergy between them provides a new hydrogen-producing active center for each material.

Synthesis and enhanced photocatalytic performance of 0D/2D CuO/tourmaline composite photocatalysts

Photocatalysis is considered to be a green and promising technology for transforming organic contaminants into nontoxic products. In this work, a CuO/tourmaline composite with zero-dimensional/two-dimensional (0D/2D) CuO architecture was successfully obtained via a facile hydrothermal process, and its photocatalytic activity was evaluated by the degradation of methylene blue (MB). Surface element valence state and molecular vibration characterization revealed that CuO chemically interacted with tourmaline via Si-O-Cu bonds. The specific surface area of the CuO/tourmaline composite (23.60 m² g^-1) was larger than that of the pristine CuO sample (3.41 m² g^-1). The CuO/tourmaline composite exhibited excellent photocatalytic activity for the degradation of MB, which was ascribed to the increase in the quantity of the adsorption-photoreactive sites and the efficient utilization of the photoinduced charge carriers. This study provides a facile strategy for the construction of 0D/2D CuO structures and the design of tourmaline-based functional composite photocatalysts for the treatment of organic contaminants in water.

Photothermal conversion assisted photocatalytic hydrogen evolution from amorphous carbon nitrogen nanosheets with nitrogen vacancies

Amorphous carbon nitrogen (a-CN) has attracted a lot of attention due to its unique properties, different from those of its crystal form. Here, we demonstrate a near-infrared (NIR) photothermal conversion assisted photocatalytic hydrogen evolution from a-CN with nitrogen vacancies (a-CNN) nanosheets. Experiments suggest that sp2 hybridized C[double bond, length as m-dash]C structures can be created in a-CNN. These structures, just like small islands, disperse on a-CNN, leading to fluorescence quenching and a superior vis-NIR light absorption. Meanwhile, these structures, like "hot islands", can generate a stronger NIR photothermal conversion. A series of in situ characterization techniques are developed to clarify the detailed mechanism of photothermal conversion assisted photocatalytic hydrogen evolution. It is found that photothermal conversion can not only accelerate the drift velocity of the photo-induced carrier, but also increase the carrier concentration, which finally promotes the photocatalytic hydrogen evolution. Due to photothermal conversion assistance, the hydrogen production rate of a-CNN nanosheets is promoted to 3.1 mmol g-1 h-1 compared to 0.71 mmol g-1 h-1 for a-CN, in which the NIR photothermal conversion is proven to contribute a 16% promotion to the hydrogen production. These findings suggest that creating an NIR photothermal conversion of photocatalysts by constructing "hot islands" can greatly promote photocatalytic hydrogen production.

The effect of n–π* electronic transitions on the N2 photofixation ability of carbon self-doped honeycomb-like g-C3N4 prepared via microwave treatment

Light harvesting is an important part of the photocatalysis process.

Double charge carrier mechanism through 2D/2D interface-assisted ultrafast water reduction and antibiotic degradation over architectural S,P co-doped g-C3N4/ZnCr LDH photocatalyst

S,P co-doped g-C₃N₄/ZnCr LDH 2D/2D heterostructure for photocatalytic ciprofloxacin degradation and H₂ evolution under the visible light irradiation.

Direct Z-scheme La1-xCexMnO3 catalyst for photothermal degradation of toluene

A series of Ce-doped LaMnO₃ (La_1-xCe_xMnO₃) were prepared and were tested for gaseous toluene oxidation in order to investigate the effect of cerium doping in LaMnO₃ on activity under photothermal conditions. It was found that the activity and CO₂ yield of the catalyst can be effectively increased when x = 0.25. A group of characterization is used to characterize the morphology, composition, and physical properties of the as-prepared catalysts. Results show that the Ce-doped LaMnO₃ can form coexistence of La_1-xCe_xMnO₃ and CeO₂, the reaction of CeO₂/La_1-xCe_xMnO₃ under photothermal conditions follows the Mars-van Krevelen redox cycle mechanism, and the prepared CeO₂/La_1-xCe_xMnO₃ can form a highly efficient Z-scheme heterojunction, which can enhance the electrons transfer speed of the catalyst. Moreover, in the photothermal catalytic degradation, lattice oxygen is the most important active substance, a small amount of cerium doping can increase the lattice oxygen content of perovskite and increase the activity of the reaction.

Iodine ion doped bromo bismuth oxide modified bismuth germanate: A direct Z-scheme photocatalyst with enhanced visible-light photocatalytic performance

A series of Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures were successfully obtained by a simple method. The Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures show outstanding photocatalytic performance for degrading the various organic pollutants of the waste water. For degradation of Tetracycline (TC), the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure exhibits the superior rate constant, which is about 7.73 times, 3.52 times and 1.66 times higher than that of the pure Bi₁₂GeO₂₀, BiOBr and I-BiOBr, respectively. Meanwhile, as we expected, the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure also displays the enhanced photocatalytic perfomance for degradation of Ciprofloxacin (CIP), 2-Mercaptobenzothiazole (MBT) and reduction of aqueous Cr(VI). The enhancement of photocatalytic performance is attributed to the high redox capacity and the strong interfacial interaction between I-BiOBr and Bi₁₂GeO₂₀, which can effectively improve the separation of photo-induced electron-hole pairs. Additionally, the photocatalytic mechanism over the Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructure is provided. The research work may provide a promising approach to fabricate other Z-scheme heterostructures with efficient photocatalytic performance.

A visible-light-driven Z-scheme CdS/Bi12GeO20 heterostructure with enhanced photocatalytic degradation of various organics and the reduction of aqueous Cr(VI)

A series of Z-scheme CdS/Bi₁₂GeO₂₀ heterostructures were successfully obtained by a simple hydrothermal method. The Z-scheme CdS/Bi₁₂GeO₂₀ heterostructures show outstanding photocatalytic performance for degrading the various organic pollutants of the waste water, and for the reduction of aqueous Cr(VI) under visible light. For degradation of 2-Mercaptobenzothiazole (MBT), the Z-scheme 30CdS/Bi₁₂GeO₂₀ heterostructure exhibits the superior rate constant, which is about 22.67 and 4.6 times higher than that of the pure Bi₁₂GeO₂₀ and CdS, respectively. Meanwhile, as we expected, the Z-scheme 30CdS/Bi₁₂GeO₂₀ heterostructure also displays the enhanced photocatalytic performance for degradation of Levofloxacin (LEV), Ciprofloxacin (CIP), Tetracycline (TC) and reduction of aqueous Cr(VI). The enhancement of photocatalytic performance is attributed to the high redox capacity and the strong interfacial interaction between CdS and Bi₁₂GeO₂₀, which can effectively improve the separation of photo-induced electron-hole pairs. Additionally, the photocatalytic mechanism over the Z-scheme CdS/Bi₁₂GeO₂₀ heterostructure is provided. The research work may provide a promising approach to fabricate other Z-scheme heterostructures with efficient photocatalytic performance.

Construction of Z-Scheme g-C3N4/RGO/WO3 with in situ photoreduced graphene oxide as electron mediator for efficient photocatalytic degradation of ciprofloxacin

Z-scheme photocatalyst g-C₃N₄/RGO/WO₃ with reduced graphene oxide (RGO) as the electron mediator was synthesized via a facile photoreduction method. According the results of photoluminescence (PL), electrochemical impedance spectroscopy (EIS) and photocurrent response, g-C₃N₄/RGO/WO₃ presents more efficient separation of charges and enhanced electronic mobility than g-C₃N₄/WO₃, g-C₃N₄ and WO₃, which benefits from the excellent electron transfer property of RGO. Reactive species trapping experiments and electron paramagnetic resonance (EPR) test demonstrated that superoxide radical (O₂^-) and hydroxyl radical (OH) were produced because of the high redox capacities caused by the unique transfer behaviors of charges in Z-scheme photocatalyst g-C₃N₄/RGO/WO₃. In the absence of RGO as electron mediator, only holes (h⁺) participates the degradation process of ciprofloxacin (CIP) due to the decreased redox capacities of g-C₃N₄/WO₃ compared with g-C₃N₄/RGO/WO₃. Therefore, the degradation rate of Ciprofloxacin (CIP) over g-C₃N₄/RGO/WO₃ composite was nearly twice as much as that over g-C₃N₄/WO₃. In addition, the analysis of intermediates provides insight into the degradation pathway of CIP.

Fabrication of surface hydroxyl modified g-C3N4with enhanced photocatalytic oxidation activity

Photocatalytic activity of C₃N₄in the decomposition of phenolic compounds in water was significantly improved with hydroxyl surface modification.