Carbon-doped TiO2 Research Articles

Non-Conventional Synthesis and Repetitive Application of Magnetic Visible Light Photocatalyst Powder Consisting of Bi-Layered C-Doped TiO2 and Ni Particles

In the current study, a non-conventional application of the magnetron sputtering technique was proposed. A four-step synthesis procedure allowed us to produce a magnetic photocatalyst powder consisting of bi-layered particles with carbon-doped TiO2 on one side, and metallic Ni on the other side. XRD, SEM and EDS methods were used for sample characterization. It was determined, that after the sputtering process optimization, the bandgap of carbon-doped TiO2 was reduced to approximately 3.1 eV and its light adsorption increased over the whole visible light spectrum. The repetitive Rhodamine B solution bleaching with magnetic photocatalyst powder and visible light showed interesting evolvement of photocatalyst efficiency. After the first cycle, Rhodamine B concentration was reduced by just 35%. However, after the second cycle, the reduction had already reached nearly 50%. Photocatalytic bleaching efficiency continued to improve rapidly until higher than 95% of Rhodamine B concentration reduction was achieved (at tenth cycle). For the next ten cycles, photocatalytic bleaching efficiency remained relatively stable. The initial gain in efficiency was attributed to the magnetic photocatalyst particle size reduction from an initial diameter of 100–150 µm to 5 µm. Naturally, the 20–30 times size reduction resulted in a remarkably increased active surface area, which was a key factor for the increased performance.

Removal of perfluorooctanoic acid by MWCNT-modified carbon-doped titanium dioxide in a peroxymonosulfate/simulated sunlight system

Perfluorooctanoic acid (PFOA) is widely used as an industrial surfactant and has been detected in various aquatic systems. Herein, a series of multiwalled carbon nanotube (MWCNT)-modified carbon-doped TiO2 catalysts (xCNT/C-TiO2) were prepared through a one-step calcination process and applied as adsorptive photocatalysts. Characterization and density functional theory (DFT) calculation results revealed that carbon doping introduced impurity energy levels between the band structures of TiO2. Moreover, the MWCNTs acted as photosensitizers that expanded the wavelength absorption range. The xCNT/C-TiO2 composites achieved efficient adsorption through multiple pathways (metal-ligand interaction, electrostatic attraction, π-anion interaction, and hydrophobic adsorption), and the adsorbed PFOA was degraded by the simulated sunlight/xCNT/C-TiO2/peroxymonosulfate (PMS) systems. The 2CNT/C-TiO2 sample exhibited the highest PFOA removal efficiency and degraded more than 90 % of the organic contaminant (2 mg/L, defluorination rate of 39.2 %) in 3.5 h. Furthermore, PFOA could be removed during repeated usage of the catalyst system without chemically regenerating the photocatalyst. The enhanced adsorption and photocatalytic removal by xCNT/C-TiO2 were due to the following reasons: (i) the MWCNTs in the composites provided a different adsorption pathway than the pre-existing monodentate mode and introduced more hydroxyl groups that could adsorb PFOA; (ii) the carbon doping in the TiO2 lattice reduced the band gap, leading to the more efficient utilization of visible light; (iii) MWCNTs inhibited the recombination of photogenerated charge carriers caused by doping, and this also promoted the production of active species and the direct oxidation of PFOA by photo-induced holes. Finally, enhanced monodentate adsorption mode and photodegradation mechanism were proposed based on experimental results and DFT calculations.

Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion

Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2.

TiO2-C nanocomposite synthesized via facile surfactant-assisted method as a part of less energy-consuming LED-based photocatalytic system for environmental applications

A novel facile method was used to incorporate carbon into the titania structure. An alternative synthesis method of carbon-doped TiO2 has been proposed by using a widely used and cheap surfactant. During the process, cetyltrimethylammonium bromide plays a dual role, as a morphology modifier and as a carbon source. The presented approach allows obtained TiO2-C nanostructures to be anatase nanocrystals with carbon being deposited either on the surface or between the TiO2 nanoparticles. The innovative nature of the research subject is related to the design of cheap LED solutions and facile synthesis of TiO2-C for use in novel energy-saving photocatalytic systems. Photocatalytic studies showed promising activity in the oxidation of 4-chlorophenol. Furthermore, it was indicated that LED-based photocatalytic systems allow a significant reduction in energy consumption compared to conventional photocatalytic sets. In addition, the high thermal efficiency of LED systems was confirmed with a thermal imaging camera. Hence, the presented novel LED photocatalytic systems can be an important part of a broad strategy for the protection of the environment.

Insights on Carbon Neutrality by Photocatalytic Conversion of Small Molecules into Value-Added Chemicals or Fuels.

Photocatalytic conversion of small molecules (including H2O, CO2, N2, CH4, and benzene) into value-added chemicals or fuels (e.g., H2, NH3, C2 +, etc.) is a promising strategy to cope with both the worldwide increasing energy demand and greenhouse gas emission in both energy sectors and chemical industry, thus paving an effective way to carbon neutrality. On the other hand, compared with conventionally thermo- or electrocatalytic processes, photoactivation can convert these very stable small molecules by the unexhausted solar energy, so leading to store solar energy in chemical bonds. Thus, it can effectively reduce the reliance on the nonrenewable fossil fuels and avoid the substantial emission of hazardous gases such as CO2, NO x , and so on while producing valued-added chemicals. For example, semiconductors can absorb solar light to split H2O into H2 and O2 or convert CO2 to alcohols, which can then be used as zero or neutral carbon energy sources. Although many efforts have already been made on photocatalytic small molecule activation, the light-energy conversion efficiency is still rather moderate and the yield of aimed value-added chemicals cannot meet the requirement of large-scale application. The core for these artificial photocatalytic processes is to discover a novel photocatalyst with high efficiency, low cost, and excellent durability. Over the past two decades, the Tang group has discovered a few benchmark photocatalysts (such as dual-metal-loaded metal oxides, atomic photocatalysts, carbon-doped TiO2, and polymer heterojunctions, etc.) and investigated them for photocatalytic conversion of the above-mentioned five robust molecules into value-added chemicals or liquid fuels. Besides, advanced photocatalytic reaction systems including batch and continuous flow membrane reactors have been studied. More importantly, the underlying reaction mechanism of these processes has been thoroughly analyzed using the state-of-the-art static and time-resolved spectroscopies. In this Account, we present the group's recent research progress in search of efficient photocatalysts for these small molecules' photoactivation. First, the strategies used in the group with respect to three key factors in photocatalysis, including light harvesting, charge separation, and reactant adsorption/product desorption, are comprehensively analyzed with the aim to provide a clear strategy for efficient photocatalyst design toward small and robust molecule photoactivation under ambient conditions. The application of in situ and operando techniques on charge carrier dynamics and reaction pathway analysis used in the group are next discussed. Finally, we point out the key challenges and future research directions toward each specific small molecule's photoactivation process.

Photocatalytic oxidative desulfurization of model fuel over visible light-active Cu-impregnated carbon-doped TiO2

TiO2 has a high bandgap energy with light absorption in the ultraviolet region making it non-efficient under visible-light. The purpose of the present work is to modify the properties of TiO2 by adding carbon and copper to its structure, in order to acquire an active nanostructure for photocatalytic oxidative desulfurization of model liquid fuel under visible light irradiation. In this regard, carbon doped TiO2 was first synthesized by a hydrothermal method, then Cu (II) were impregnated on carbon doped TiO2. The resulting photocatalysts were characterized by techniques such as XRD, N2 physisorption, SEM, TEM, DRS, EDX, PL, and FTIR. The effects of parameters including calcination temperature (200–600 °C), Cu loading (0.5–5 wt%), amount of H2O2 oxidant (0–3 ml), the volume ratio of solvent to fuel (0.5–2), initial concentration of DBT (100–1000 mg/ml) and the catalyst dosage (1–4 g/l) on the performance of the photocatalyst were subsequently studied. The best performance (98.27% of DBT removal efficiency) was obtained for 0.5Cu-CT in presence of 0.1 ml H2O2, solvent to fuel ratio of 1, catalyst dosage of 2 g/l, and initial DBT concentration of 250 mg/l 0.5Cu-CT demonstrated the best photocatalytic activity due to low electron/hole recombination, high BET surface, and appropriate bandgap energy.

Room-temperature MXene-derived Ti3+ and rich oxygen vacancies in carbon-doped amorphous TiOx nanosheets for enhanced photocatalytic activity

Exploring efficient photocatalysts for photocatalytic degradation is of considerable importance for the long-term mitigation of environmental stress. Although defect engineering is an effective strategy to alter the electronic transport properties and light absorption capacity of TiO2, the synthesis of TiO2 rich in oxygen vacancies (OVs) via a green process at room temperature and with low energy consumption remains a challenge. Herein, amorphous TiO2 nanosheets rich in OVs were prepared by H2O2-assisted room-temperature oxidation of Ti3C2Tx MXene via a bottom-up approach. Notably, small amounts of C and Ti3+ were introduced during the preparation of carbon-doped TiO2 (C-TiOx), which was shown to possess abundant surface functional groups (e.g., –OH, –O, and –F) and two intermediate levels in its bandgap. Comparative experiments demonstrated that OVs play a key role in suppressing the recombination of photogenerated carriers and expanding the light absorption range of the photocatalyst. The unique quasi-two-dimensional structure of C-TiOx features a large number of exposed active sites, which are beneficial for improving its catalytic performance. Tetracycline (TC) was removed from the aqueous solution by the prepared photocatalysts C-TiOx and annealed-TiO2, and the former adsorbed 41.1% of TC. The TC removal efficiency of C-TiOx was 76%, which was higher than that of annealed-TiO2. This approach embodies a new strategy for introducing defects and doping in TiO2. Moreover, it is also thought that C-TiOx possesses promising characteristics suitable for a wide range of potential future applications.

Electrocatalytic CO2 Reduction at Pyridine Functionalized Au Nanoparticles Supported by NanoCOT Electrode

CO2 reduction reaction (CO2RR) is a promising technique for mitigating global warming and storing renewable energy if it can be obtained with a highly selective, efficient, and durable electrocatalyst. Here, we report CO2RR catalyzed by Au nanoparticles (NPs) stabilized by pyridines and pyrimidines (e.g., 2-mercaptopyridine (2Mpy), 4-mercaptopyridine (4Mpy), and 2-mercaptopyrimidine (2Mpym)) on a nanostructured carbon-doped TiO2 nanowire (NanoCOT) electrode, which has been previously reported by our team for electrocatalytic water oxidation. An online gas chromatography (GC) set-up with improved gaseous product sensitivity with real-time pressure monitoring is used to quantify CO and hydrogen products from the Au NP-modified NanoCOT electrode. High CO selectivity is observed at Au-2Mpy coated NanoCOT electrode. CO2 reduction products are not observed at bare NanoCOT suggesting CO2 is reduced at the Au nanoparticle sites of the electrode. Moreover, CH3OH is not detected at the Au-Mpy/Mpym NPs during rotating ring disk electrode (RRDE) analysis which implies pyridine attached to the Au NPs has no catalytic effects on CO2RR as claimed by others in the literature. A durable complete H-cell using a NanoCOT anode and Au NP-NanoCOT cathode electrodes is assembled for complete water splitting, CO2RR, and stability test.

Ti3C2 MXene derived carbon-doped TiO2 multilayers anchored with Fe2O3 nanoparticles as anode for enhanced lithium-ion storage

Transition-metal carbides, carbonitrides, and nitrides (MXene) as an emerging two-dimensional semiconductor has open an ideal pathway for fabricating various TiO2-based functional materials. In this work, we demonstrate a simple and one-step heat treatment for the fabrication of Ti3C2 MXene-derived carbon-doped TiO2/Fe2O3 composite for superior lithium-ion batteries (LIBs). As an anode, the as-fabricated composite delivers an excellent lithium-ion storage of 538 mA h/g at a current density of 0.1 A/g and superior rate performance of 152.6 mA h/g at a higher current density of 5 A/g, which is 6 times higher than that of C-doped TiO2 electrode. In addition, a remarkable cyclic stability with 88.46 % capacity retention is also obtained for the composite anode at a current density of 1 A/g after 1000 cycles. Based on various characterizations, the greatly enhanced electrochemical performance can be attributed to the synergistic effects of carbon doping, layered structures of TiO2, and the anchoring of Fe2O3 nanoparticles, which effectively promote the charge transport kinetics. This study will broaden the Ti3C2 MXene application in LIBs and meanwhile provide an alternative method for synthesizing more efficient anode materials.

Fabricating Z-scheme C-doped TiO2/rGO nanocomposites for enhanced photocatalytic NO removal

It is attractive to explore practical approaches to optimize the photodegraded NO property of TiO2. Herein, a typical Z-shaped heterojunction C-TiO2/rGO composed of carbon-doped TiO2 and reductive graphene oxide (rGO) was constructed to optimize the NO removal efficiency through an in situ one-pot hydrothermal process with glucose as reductant and dopant. The C-TiO2/rGO (0.11%) composite displays a remarkable NO removal performance of 40.6% under visible light illumination. It was found that the C-TiO2 nanoparticles were tightly attached to the rGO sheets and had strong interactions with rGO, which induced a positive impact on not only the light absorption and photo-generated charge separation but also the NO adsorption and reactive oxygen species formation, resulting in boosted photodegrade NO activity. As to the photodegrade NO process over the C-TiO2/rGO, the HO• and O2 •− were the dominant radicals, of which the O2 •− radical originated from the interactions between C-TiO2 and rGO. We proposed a Z-scheme mechanism to illuminate the advanced photocatalytic activity of C-TiO2/rGO. This work affords an approach to developing effective photocatalysts in the NO purification field.

Exploring the mechanism of room temperature ferromagnetism in C-doped TiO2 nanoclusters by tuning the defects by different annealing temperature using citric acid as C source

Revealing the mechanism of room temperature ferromagnetism (RTFM) in carbon-doped TiO2 (C–TiO2) is critical to accelerate the development of TiO2-based spintronic devices. Herein, C–TiO2 nanoclusters were prepared by a sol-gel process using citric acid as C source, and the defects and RTFM of the samples were tuned by vacuum annealing at different temperature, and then the mechanism of RTFM induced by C doping is studied. Results revealed that with the increase of annealing temperature, residual organic precursor was gradually removed, and the phase transformed from pure anatase to rutile and brookite, followed by the precipitating of elemental C at 600 °C and 700 °C. Due to the doping of C, defects including substitutional C atoms for Ti sites (CTi), interstitial C atoms (Ci) and oxygen vacancy were introduced into the lattice. The concentration of CTi increases first till 500 °C, and then decreases gradually with the annealing temperature, while that of Ci exhibits opposite trend, and the oxygen vacancy concentration raises continuously. Influenced by the annealing temperature, RTFM of the samples exhibits similar trend to that of CTi, and the saturation magnetization (Ms) reaches the maximum at 500 °C. The RTFM is synergistically induced by CTi and oxygen vacancy, and ferromagnetic p-p coupling interaction trigged by CTi plays a more critical role. The results provide a significant reference for tuning the defects and RTFM in C–TiO2.

Well-designed MXene-derived Carbon-doped TiO2 coupled porous g-C3N4 to enhance the degradation of ciprofloxacin hydrochloride under visible light irradiation

In this work, using melamine and MXene powder as precursors, NH4Cl as a template, a novel S-scheme heterojunction composite material g-C3N4/C-TiO2 was synthesized by a one-step calcination method. During the calcination process, the gas template NH4Cl played a dual role, which not only striped the massive g-C3N4 into porous flakes with a larger specific surface area but also striped the agglomerated MXene derivatives (C-TiO2) nanoparticles, making them bind more closely with g-C3N4. The charge separation efficiency and photocatalytic performance were greatly improved due to the formation of heterojunction and the larger specific surface area of the sample. Within 50 min, the g-C3N4/C-TiO2 exhibited high photocatalytic performance toward ciprofloxacin hydrochloride (CIP·HCl) with degradation efficiencies of 88.14% under visible light (λ ≥ 420 nm), which was 8.9 times higher than that of pure g-C3N4. In addition, we also used a series of characterizations to confirm the mechanism of S-scheme heterojunction and inferred the possible CIP photodegradation pathway.

Adsorptive Capacity Study of Mesoporous Carbon-Doped TiO<sub>2 </sub>and its Application in Cu(II) Removal from Water

Mesoporous carbon-doped TiO2 (MCT) was synthesized via a template-free method in combination with solvothermal treatments. The structure, particle size and composition of this adsorbent were measured using XRD, TEM and XPS. Also, the usability of isothermal models for Cu (II) onto mesostructured adsorbent was implicated in these cases. The adsorptive capacity of MCT for Cu (II) was assessed using ICP-MS technique. The maximal adsorptive capacity was 16.9 mg g-1, and the ion-exchange action of Cu (II) was found to be the predominant adsorption.

Solar light-driven photocatalytic degradation of methyl blue by carbon-doped TiO2 nanoparticles

Sol-gel method was used to synthesize carbon doped TiO2 nanoparticles with excellent photocatalytic activity under solar light irradiation. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrophotometer (FTIR), and UV–vis spectrometer were used to analyze the absorption spectra and methyl blue concentration in water at different time intervals throughout the photodegradation experiment. The results revealed that pure TiO2 and carbon doped TiO2 nanopowders are anatase phase with crystallite sizes ranging from 8 to 13 nm. The doping was found to decelerate the grain development of the nanopowder. Although carbon doping in TiO2 may effectively expand the light absorption capabilities towards visible light, too much doping is deleterious to light absorption ability. The optimal doping quantity for maximum photocatalytic degradation of MB in our experiment was 2 atoms %; above this doping, the catalyst's photocatalytic activity diminishes.

Sol-Gel Synthesis and Characterization of Carbon doped TiO2 based on Solanum Tuberosum Starch

The carbon-doped TiO2 have been synthesized through sol-gel method using Solanum tuberosum starch as carbon source. The carbon precursor composition and reaction time were varied to study its influence to the crystal structure and electronic structure of resulted material. The C- TiO2 product was characterized by XRD, UV-Vis DRS, FTIR, and photocatalytic activity examine by methylene blue degradation. The results showed that variations in the composition of the carbon precursor and reaction time affected the characteristics of the crystal structure and photocatalyst activity of C- TiO2. The optimum variation was found in the variation of 1.5 gram carbon composition and 24 hours hydrolysis time which had the smallest particle size and lowest bandgap energy. The highest photocatalyst activity was obtained at a 24-hour reaction time variation with 59.375% percent of methylene blue degraded in the second-order reaction with a k value of 2.1351.

Highly efficient visible light photocatalysis of tablet-like carbon-doped TiO2 photocatalysts via pyrolysis of cellulose/MIL-125(Ti) at low temperature

In this work, the tablet-like carbon-doped TiO2 photocatalysts (CM-x) were successfully fabricated via the pyrolysis of cellulose/MIL-125(Ti) at low temperature. All carbon-doped TiO2 photocatalysts are characteristic of strong response in the visible-light region. When the pyrolysis temperature is 350 ​°C, the degradation efficiency of tetracycline (TC) over carbon-doped TiO2 photocatalysts (CM-350) is 100% under optimal conditions (catalyst dosage ​= ​0.5 ​g/L, TC concentration ​= ​15 ​mg/L, pH ​= ​6, T ​= ​20 ​°C). The excellent photocatalytic performance is closely related to carbon doping, the residual organic groups, high BET surface area, abundant oxygen vacancies and low rate of carrier recombination. Superoxide radical (•O2−) and hole (h+) are the dominant active species in the entire photocatalytic process. The novel tablet-like carbon-doped TiO2 photocatalyst through the pyrolysis of cellulose/MIL-125(Ti) at low temperature will be more promising for rapid degradation of organic pollutants in water.

Unveiling the structural, electronic, and optical effects of carbon-doping on multi-layer anatase TiO2 (1 0 1) and the impact on photocatalysis

Carbon-doped (C-doped) TiO2 has demonstrated effective photocatalytic activity in the visible-light region. Here, we make use of density functional theory (DFT) methods to understand the photocatalytic activity of C-doped anatase-TiO2 (101) surfaces as a function of layer thickness. The formation energy results show that C-doped O sites (CO) are more stable in the bulk than in the subsurface or on the surface, while C-doped Ti sites (CTi) are more stable on the surface than in the bulk or subsurface. CO defects introduce impurity states in the band gap, do not affect the band gap energy, and induce an electron trap close to the conduction band edge and enhances light absorption in the visible and IR spectrum. CTi defects induce structural distortions caused by a CO covalent bond with no impurity states formed in the band gap although there is a reduction in the band gap energy, which leads to a red-shifted absorption. These results shed insight on how carbon doping influences the electronic and optical properties of anatase that can be implemented in the design of semiconductor materials with high photocatalytic activity.

Visible-Light-Driven Carbon-Doped TiO2-Based Nanocatalysts for Enhanced Activity toward Microbes and Removal of Dye.

Solar-driven photocatalytic approach is an attractive, clean, and effective way for decontamination of water. In this work, visible-light-activated TiO2 nanoflakes (TNFs) and carbon-doped TiO2 nanoflakes (C-TNFs) were synthesized via a facile hydrothermal route using different carbon sources. The as-synthesized nanostructures were successfully characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), critically disclosing the anatase nature containing titanium–oxygen having flake/platelet-like morphology with ∼32 nm in size, respectively. The photocatalytic activity was characterized via the degradation of methylene blue (MB) and bacterial inactivation of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The experimental results showed that C-TNFs significantly enhanced photocatalytic activity compared to bare TNFs. It was found that TNF nanocatalysts exhibited superior photocatalytic activity against photodegradation of MB (92.7%) and antibacterial activity (85.6%) under sunlight irradiation. In addition, reduced graphene oxide (RGO)-TNFs have a good recycling ability and are expected to be a promising candidate for photocatalytic applications under sunlight. Consequentially, the higher activity of RGO-TNF nanocatalysts under sunlight irradiation for organic degradation and bacterial inactivation implies that hydrothermal synthesis allows for the preparation of efficient and low-cost carbon-doped photocatalysts for the photodegradation of a wide range of environmental pollutants.

Development of activated carbon-doped TiO2 nanoparticle thin film for application in dye-sensitized solar cells

Carbon This research aims to study the preparation of activated carbon-doped TiO2 nanoparticle thin films with basellaceae, malvaceae and hylocereus dyes for application in dye-sensitized solar cells (DSSCs). The physical and chemical properties of as-prepared thin films were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectra (UV-vis DRS) techniques. Results revealed that the basellaceae dye (JSC is 13.5 mA/cm2, VOC is 0.450 V and η (%) is 1.59) on thin film showed the highest efficiency compared with the malvaceae (JSC is 10.2 mA/cm2, VOC is 0.425 V and η (%) is 1.08) and hylocereus (JSC is 12.1 mA/cm2, VOC is 0.325 V and η (%) is 1.17) dyes. Moreover, we observed that activated carbon/TiO2 nanoparticle thin film exhibited a higher efficiency than other thin film samples. This might be due to the activated carbon doped into the TiO2 leading to facilitate the separation of photogenerated charge carriers, resulting in its enhanced efficiency.

Well-Designed Mxene-Derived Carbon-Doped Tio2 Coupled Porous G-C3n4 to Enhance the Degradation of Ciprofloxacin Hydrochloride Under Visible Light Irradiation

Well-Designed Mxene-Derived Carbon-Doped Tio2 Coupled Porous G-C3n4 to Enhance the Degradation of Ciprofloxacin Hydrochloride Under Visible Light Irradiation