
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)11860-9
10.1016/j.heliyon.2024.e35829
e35829
Research Article
Enhancing the photocatalytic efficiency of g-C3N4 for ciprofloxacin degradation using Tetrakis (acetonitrile) copper(I) hexafluorophosphate as a highly effective cocatalyst
Nejat Razieh organochem.nejat@kub.ac.ir

Department of Chemistry, Kosar University of Bojnord, Bojnord, Islamic Republic of Iran
15 8 2024
30 8 2024
15 8 2024
10 16 e3582915 6 2024
3 8 2024
5 8 2024
© 2024 The Author. Published by Elsevier Ltd.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Ciprofloxacin antibiotic (CP) is one of the antibiotics with broad-spectrum antimicrobial activity that has the highest rate of antibiotic resistance. This antibiotic undergoes incomplete metabolism within the human body and is excreted into the water, resulting in its hazardous biological and ecotoxicological effects. In this study, a novel photocatalyst, comprised of graphitic carbon nitride (g-CN) and Tetrakis(acetonitrile)copper(I)hexafluorophosphate ([(CH3CN)4Cu]PF6), denoted as CuPF6/g-CN, was employed for the degradation of ciprofloxacin under visible-light irradiation. The Cu complex, functioning as a co-catalyst, assumes a crucial role in facilitating the efficient separation of photogenerated charges and exhibiting high absorption in the visible-light region. More surprisingly, CuPF6/g-CN does surpass by up to 6 times the behavior reached with bare g-CN. The experimental findings indicated that the optimal degradation of ciprofloxacin (CP) occurred after 50 min when using a concentration of 20 mg L−1 CP and a concentration of 0.05 g/L CuPF6/g-CN, under a pH of 8. This research offers valuable insights into the advancement of cost-effective co-catalysts that enhance the photocatalytic capabilities of established photocatalysts. It contributes to improving the overall performance and efficiency of these photocatalytic systems.

Graphical abstract

Image 1

Highlights

• Proving the promising role of Cu + for Ciprofloxacin Degradation.

• Degradation of Ciprofloxacin under visible light irradiation.

• The Cu+/C3N4 composite with electronic structural property as visible-light active photocatalyst.

Keywords

Cu
G-C3N4
Photocatalyst
Antibiotic
==== Body
pmc1 Introduction

Photocatalytic technology, being recognized as a highly favorable and promising process, holds great potential in addressing the escalating issue of water pollution. Through its safe and environmentally friendly approach, it offers an effective solution for the decomposition of organic pollutants, contributing to the mitigation of water pollution in a sustainable manner [1,2]. The core of the process of photocatalytic degradation is the design and fabrication of high-performance, eco-friendly, and economically viable photocatalytic materials. Materials with semiconductor properties are extensively employed as the predominant photocatalysts in various applications owing to their distinctive surface electronic, physical, chemical, optical, and redox properties [3]. g-CN as a metal-free and cost-effective organic semiconductor, stands out among these materials with its exceptional photocatalytic properties, due to great band structure, good thermal stability, non-toxicity, and tunable electronic structure [4,5].

Several studies have demonstrated that in comparison to bulk g-CN, the g-CN nanosheets (NS), have larger surface area and higher solubility in water and thus C3N4-NS have been applied in broad fields such as photocatalysis, electrochemical sensors, fuel cells, and fluorescence applications [[6], [7], [8], [9], [10], [11]], Nevertheless, the large bandgap implying weak solar light absorption, the high photogenerated carrier recombination rate, and the inability to produce reactive species by the photogenerated holes (h+) [12,13], hydroxyl radical have limited the use of g-CN in photocatalytic activity. One of the most significant strategies used to overcome these problems expressively and improve the effectiveness of g-CN photocatalysis is assembling the pristine g-CN with metal oxides [14], metallic elements [15], semiconductors [16,17], and magnetic nanoparticles [18].

In various methods explored, the use of co-catalysts is particularly important for simplifying the charge acceptance by species in solution and facilitating the redox reactions. Among several candidates, the heterojunction of g-CN with visible-light sensitizing Cu complex can be an excellent suggestion with a high absorption coefficient within the solar spectrum and low processing cost. Moreover, Cu metal is a cheap, nontoxicity, and abundant element [19,20], and the cu element has been investigated for photolysis application in various research [[21], [22], [23], [24], [25]].

On the other hand, the use of antibiotics as important clinical drugs has marked a new era of drugs for infectious illness therapy or other diseases in humans and animals [26,27]. The wide use of various antibiotics in order to treat infections and prevent diseases in animals has revolutionized in livestock, poultry, aquaculture, and cultivation industry [[28], [29], [30]]. However, arbitrarily and the overuse use of antibiotics leads to the production of untreated discharge and these antibiotic residues cause drug resistance which poses a significant threat to the ecological environment.

CP as a third generation and synthetic antibiotic belongs to the fluoroquinolone group of antibiotics which exhibits broad-spectrum antimicrobial activity but, unfortunately, CP is not able to be efficiently metabolized in the human body because of high structural stability, and thus, the residues are diffuse to the environment [31]. In addition, expired CP antibiotics as wastes are released into the natural environment [32] In general, the presence of CP in water and wastewater is a serious problem due to its toxicities and can accumulate in the organism.

In this research, we have synthesized ([(CH3CN)4Cu]PF6) modified g-CN photocatalyst (CuPF6/g-CN) for the destruction of CP in water in VIS light. Results show that the pure g-CN almost exhibits a partial reduction of CP concentration (about 10 %) during the photocatalytic process, and also, the photocatalytic performance of ([(CH3CN)4Cu]PF6) salt, and g-CN modified with CuO was less of CuPF6/g-CN. The results demonstrate the incorporation ([(CH3CN)4Cu]PF6) molecules with g-CN resulted in improved light absorption spectrum of the carrier and photocatalytic activity due to its high surface area. Tetrakis(acetonitrile)copper(I) hexafluorophosphate is a useful source of unbound Cu(I).

2 Experimental section

All the materials, including thiourea, HPF6, CH3CN, ethanol, copper (I) oxide and acetonitrile were in analytic grade, prepared by Merck, Fluka, and Sigma-Aldrich chemical company, and used without further purification. X-ray diffractometry, XRD Philips PW1730 (using Cu Kα radiation (α = 0.154056 Å), was used for phase purity and crystalline structure analysis of samples. Fourier transform infrared spectra (NICOLET IR100 FT-IR with spectroscopic grade KBr) were obtained within the 400-4000 cm−1 range. The Thermo Scientific Evolution 300/600 UV–Visible spectrophotometer (USA) was utilized to acquire the UV–vis diffuse reflectance spectra (DRS) of the samples. A Philips XL-300 was employed to perform the field emission scanning electron microscopy (FESEM) analysis. To determine the specific surface areas, the BET method was employed using the Micromeritics Instrument Corporation TriStar II. UV–visible absorption spectra were acquired at room temperature using a Shimadzu UV-2550-8030 spectrophotometer in the range 190–800 nm with a slit width of 5.0 nm. The light source employed had a wavelength of 360.0 nm. A 400 W lamp, specifically a high-pressure mercury-vapor lamp emitting light with a cutoff filter at 420 nm (SCF–S50-42 L; Sigma Koki, Japan., was utilized to provide the visible illumination.

2.1 The synthesis of the photocatalyst

First, g-C3N4 was synthesized by annealing thiourea at 550 °C for 3 h with the heating rate of 5 °C min−1 [33]. Tetrakis(acetonitrile)copper(I) hexafluorophosphate molecules were prepared following a previously published method [34]. To synthesize CuPF6/g-CN, the g-CN (1.0 gr) in 60 ml of ethanol were added and sonicated (2 h) to make the thick slurry. Then, ([(CH3CN)4Cu]PF6) (0.05 g) was added to the formed yellowish heterogeneous solution and for a duration of 24 h, the mixture underwent continuous stirring. In the final step, the cap was removed from the reaction vessel, and the solid phase was separated by filtration, it was then subjected to a drying process at 80 °C.

2.2 Characterization of the catalyst

Fig. 1 illustrates the XRD measurements of g-CN and CuPF6/g-CN materials, shedding light on the presence, crystallinity degree, and purity of both g-CN and the catalyst. The X-ray diffraction (XRD) pattern of g-CN exhibited a prominent peak at 2θ = 27.5°, which corresponds to the (002) planes (JCPDS No. 87–1526). This peak is characteristic of the interplanar stacking structure commonly observed in graphitic materials [35,36]. Furthermore, a secondary diffraction peak at 2θ = 13.1° was identified as corresponding to the (100) planes. The relatively good intensity of this peak provides further evidence for the presence of a graphite-like structure in the g-CN material [[37], [38], [39]]. Importantly, the characteristic peaks [Cu(CH3CN)4]PF6 of g-CN remained weaker in the spectrum of the catalyst, indicating the successful loading of [Cu(CH3CN)4]PF6 onto the g-CN material. The observed diminution in the intensity of the g-C3N4 diffraction peaks within the catalyst spectrum suggests the possibility of structural alterations to the g-C3N4 lattice arising from the modification process. Additionally, the emergence of new peaks at 2θ = 43.3° and 50.4°, corresponds to the (111) and (200) planes of the elemental copper phase (JCPDS card 04–0836).Fig. 1 XRD of g-CN, CuPF6/g-CN and CuPF6.

Fig. 1

FT-IR spectroscopy was employed to analyze the molecular vibrations and functional groups of (2a) g-CN and (7b) CuPF6/g-CN in the range of 400–4000 cm−1 (Fig. 2). The chief peaks for pure g-CN appear between 1200 and 1700 cm−1, corresponding to the stretching vibration of CN heterocycles. Another significant band is observed at 800 cm−1, indicative of the breathing vibration of Tri-S-triazine units. The peaks in the range of 3150–3300 cm−1 originate from the stretching vibration of N–H bonds [40]. In pure [Cu(CH3CN)4]PF6 (CuPF6), a prominent characteristic band is detected at 2427 cm−1 which can be allocated to the vibration of the coordinated acetonitrile ligands. Additionally, the principal peaks observed within the range of 550–900 cm−1 can be ascribed to the vibrational modes of the PF6 counter ion (2c). The FT-IR spectrum of CuPF6/g-CN retains all characteristic vibrational peaks of g-CN, including the bands attributed to CN bonds at 2327 and 2348 cm−1. Additionally, distinct peaks corresponding to PF6 vibrations are observed at 804 and 591 cm−1 [41]. The presence of a small amount of [Cu(CH3CN)4]PF6 on the g-CN material in the CuPF6/g-CN spectrum leads to a reduced intensity of the specific g-CN bands. (Fig. 2b).Fig. 2 FT-IR Analysis: (a) g-CN, (b) CuPF6/g-CN and (c) CuPF6 Spectra.

Fig. 2

Fig. 3 illustrates the UV–Vis diffuse reflectance spectra (DRS) of the synthesized g-CN and CuPF6/g-CN, providing insights into their respective optical properties. The addition of [Cu(CH3CN)4]PF6 particles on the g-CN surface increased the absorbance of CuPF6/g-CN. This higher absorbance indicates the generation of more electron-hole pairs under visible light, potentially enhancing the photoactivity of the material.Fig. 3 UV–Vis DRS of a) g-CN, CuPF6/g-CN, and b) CuPF6.

Fig. 3

Fig. 4 showcases the SEM images of the g-CN support (Fig. 4a) and CuPF6/g-CN catalyst, providing insights into their respective morphologies. In Fig. 4b, it is evident that the g-CN material is decorated with crystals, indicating successful loading of [Cu(CH3CN)4]PF6 onto the g-CN support (Fig. 4b).Fig. 4 SEM Analysis: (a) g-CN and (b) CuPF6/g-CN Morphologies.

Fig. 4

The successful incorporation of [Cu(CH3CN)4]PF6 onto the surface of g-C3N4 is further evidenced by the TEM images presented in Fig. 5. This figure demonstrates that the CuPF6/g-CN nanocomposite is composed of a significant quantity of [Cu(CH3CN)4]PF6 particles, which occupy a substantial fraction of the available surface area on the g-C3N4 material. The g-C3N4 substrate serves as a matrix within which these [Cu(CH3CN)4]PF6 particles are successfully integrated and uniformly distributed. This observation corroborates the effective integration and even dispersion of the [Cu(CH3CN)4]PF6 species within the g-C3N4 matrix.Fig. 5 TEM image of CuPF6/g-CN.

Fig. 5

Energy-dispersive X-ray spectroscopy (EDS) was recorded and shown in Fig. 6. In the EDS spectrum of the catalyst, all the peaks related to Cu, P, C, N, and C were observed.Fig. 6 EDS spectrum of the catalyst.

Fig. 6

Nitrogen adsorption-desorption isotherm measurements were conducted to provide insights into the catalyst's pore structure and textural properties (Fig. 7). The nitrogen adsorption-desorption isotherms demonstrated a class IV mixture as per the IUPAC classification, characterized by a H3 hysteresis loop. The presence of hysteresis loops within the relative pressure range of 0.35–0.97 suggests that the samples possess a mesoporous structure in their porous network. As reported in previous studies, the pure g-CN material exhibited a low BET surface area of 10.2 m2/g [42,43] and after [Cu(CH3CN)4]PF6 was loaded on g-CN, the BET surface area of g-CN experienced a significant increase to 17.64 m2/g. The catalyst's specific surface area was determined using the BET method, yielding a value of (specific surface area value) m2/g (Fig. 7a). The pore size distribution was Pore size = 1.64 nm and a pore volume of 0.118 cm3/g (Fig. 7b).Fig. 7 N2 sorption isotherms of photocatalyst (a), pore diameter distribution curve of photocatalyst (b).

Fig. 7

Mott-Schottky plots were leveraged at a frequency of 500 Hz to scrutinize the band-edge potentials of the g-C3N4 and CuPF6/CN photocatalysts (Fig. 8a). Fig. 8a displays the plots, and the positive slope observed in the curves denotes that both the g-C3N4 and CuPF6/CN exhibit the characteristic n-type semiconductor behavior. As a result, the extrapolated conduction band (CB) positions of g-C3N4 and CuPF6/CN samples stand at −0.95 V and −0.97 V, correspondingly (vs Ag/AgCl, pH = 7). Based on the band gaps of the g-C3N4 (2.84 eV) and CuPF6/CN (2.59 eV), the valence band (VB) positions are calculated to be 1.62 V and 1.89 V, respectively. It was observed that the ECB changed to more negative for g-C3N4 after Cu modification, suggesting that CuPF6/CN retained the strong redox ability of the photogenerated electrons. Fig. 8b displays electronic band structures for g-C3N4 and CuPF6/g-CN.Fig. 8 (a) Mott-Schottky curves and (b) electronic band structures for g-C3N4 and CuPF6/g-CN.

Fig. 8

The stability and recoverability of the catalyst were evaluated during the degradation of ciprofloxacin under visible-light irradiation. After each reaction, the catalyst was separated, washed with deionized water, dried, and then directly reused in the next run. It was observed that the recovered catalyst could be recycled in subsequent runs without a significant decrease in activity, even after the sixth run (Fig. 9).Fig. 9 Reusability of the CuPF6/g-CN for degradation of ciprofloxacin under visible-light irradiation.

Fig. 9

2.3 Photocatalytic experiments

The evaluation of the photocatalytic activities of CuPF6/g-CN involved using a catalyst mass of 0.05 g, 2 mmol of 33 % H2O2, and a reaction mixture containing 50 ml of an aqueous medium with a concentration of CP (20 mg L−1). To maintain the adsorption-desorption equilibrium between CP and the catalyst surface, an adsorption reaction was initiated by subjecting the CP solution to magnetic stirring in the dark for a duration of 30 min. The solution was exposed to irradiation for a period of 50 min using a 400 W lamp (a high-pressure mercury vapor lamp emitting light at a wavelength of 546.8 nm). To avoid any potential thermal catalytic effects, the temperature of the photocatalytic reaction was carefully controlled and maintained between 25 and 30 °C. Cooling fans were employed to regulate and stabilize the temperature throughout the reaction. After 10 min, a sample of approximately 5 mL was extracted from the reaction mixture and subjected to centrifugation to separate the catalysts from CP. The resulting supernatant, containing the CP, was measured by UV spectrophotometer.

Fig. 10 displays the UV–Visible absorption spectra of CP degradation using CuPF6/g-CN under VIS light at pH 8. The spectra exhibit a maximum absorption band at 275 nm, indicating the absorption of light during the degradation process. Fig. 10 demonstrates the decrease in the absorption peak at 275 nm and the shoulder at 322 nm as the degradation progresses. After 50 min of irradiation, the degradation efficiency reached an impressive 98.5 %, indicating the successful photodegradation of CP using the photocatalyst.Fig. 10 UV–visible absorption spectra of CP elimination with CuPF6/g-CN (CP) = 20 mg L−1, [cat.] = 0.05 g, H2O2 (2 mmol), pH = 8).

Fig. 10

Table 1 presents a comparison of the results from the current work with the results reported in similar articles investigating the degradation of antibiotics [[44], [45], [46], [47], [48], [49]]Table 1 comparison of the results from the current work with the results reported in similar articles.

Table 1Entry	Catalysts	Modification	Light source (lamp)	Band gap (eV)	Antibiotics (mg/L)	Performance over pristine g-C3N4	Ref.	
1	La-g-C3N4	Metal doping	18 UV (λ: 400–800 nm)	2.63	TC (10)	5.6	[44]	
2	Cl-g-C3N4	Non-metal doping	300 Xenon (λ > 420 nm)	2.70	TC (10)	2.4	[45]	
3	Er (III)-g-C3N4	Metal doping	35 W Xenon (−)	2.4	TC (25)	1.7	[46]	
4	Ba-g-C3N4	Metal doping	150 W Xenon (λ > 400 nm)	2.56	TC (20) mg/L	2.8	[47]	
5	Ag/g-C3N4	Metal NPs decoration	300 W Xenon (λ > 420 nm)	2.72	TC (20)	3	[48]	
6	Cu/O-g-C3N4	Co-doping	300 W Xenon (λ > 420 nm)	2.28	LEVO (15)	6.2	[49]	

3 Results and discussion

3.1 Optimizing photocatalytic performance: reaction conditions for CuPF6/g-CN composite

Fig. 11 showcases the combined effect of light irradiation and the catalyst on CP degradation, providing insights into their influence on the efficiency of the process. In the absence of the catalyst under visible (VIS) light irradiation, no degradation of CP is observed. However, a partial reduction in CP concentration (approximately 10 %) is observed when the catalytic reaction is conducted in the dark. This partial reduction is likely attributed to the partial adsorption of CP molecules onto the surface of the catalyst. The degradation efficiency is significantly enhanced up to 98.5 % when the CP solution containing the catalyst is exposed to visible (VIS) light irradiation.Fig. 11 Impacts of VIS light, g-CN, cat. and, (VIS light + cat.) on CP degradation.

Fig. 11

Moreover, the effect of various VIS light-driven catalysts on CP degradation were examined (Fig. 12). The reference photocatalysts chosen for the study included CuO/g-CN, pristine g-CN, and [Cu(CH3CN)4]PF6 salt, and their photoactivity was investigated by catalyzing the degradation of CP in water. Obviously, the photocatalytic activity of CuPF6/g-CN was found to be significantly higher compared to pure g-CN and [Cu(CH3CN)4]PF6 salt and also, CuPF6/g-CN shows higher catalytic activity than CuO/g-CN for CP degradation under VIS light. This indicates that the introduction of the ([(CH3CN)4Cu]PF6 salt enhances the photoactivity of the g-CN catalyst by absorbing well in the VIS light region, exhibiting superior adsorption towards CP molecules, and efficiently separating the photogenerated charges.Fig. 12 Effects of various VIS light-driven catalysts on CP degradation.

Fig. 12

Fig. 13 demonstrates the influence of pH on the degradation of CP antibiotic in an aqueous solution. Based on the findings depicted in Fig. 13, the elimination of the CP at pH = 8 was complete after 50 min. The interaction strength between the catalyst and CP can influence the efficiency of Fenton reactions which is related to the pH conditions. Normally, CP molecules acquire positive and negative charges when introduced into acidic and basic solutions, because CP molecules accept and lose a hydrogen ion (H+) respectively [50]. On the other hand, the acid-base properties of catalyst surfaces play a crucial role in governing the adsorption-desorption dynamics and the overall photocatalytic degradation performance [51]. pH levels ranging from 4 to 10 were investigated in the study. The degradation of CP is favored at slightly weak basic conditions because more CP molecules exhibit adsorption on the catalyst surface. The surface characteristics of catalysts play a crucial role as the reactions predominantly occur on their surfaces.Fig. 13 Impact of Solution pH on CP Degradation in the Presence of CuPF6/g-CN.

Fig. 13

Fig. 14 demonstrates a positive correlation between the CP removal rate and the catalyst dosage within the range of 0.03 g/L to 0.15 g/L. The reaction exhibits the highest yield when utilizing 0.1 g of catalyst under VIS light irradiation, and reducing the amount of catalyst results in a decrease in yield, while further increasing the catalyst dosage leads to negligible improvement in the yield.Fig. 14 Effect of the catalyst dosage for CP degradation by CuPF6/g-CN.

Fig. 14

3.2 Possible oxidation mechanism

Herein, we report a postulated mechanism of combining our experiment results with related studies [52,53]. The results indicated that the coordination between Cu+ and graphitic carbon nitride nanosheets resulted in enhanced generation of reactive oxygen species (ROS) upon exposure to light (Scheme 1, Scheme 2). Probably, the integration of Cu+ with g-CN would enhance the pro-oxidant effect. Cu+–g-CN, serving as the redox-active species, exhibited the ability to catalyze the reduction of molecular oxygen to produce both superoxide anions and hydrogen peroxide. These reactive species, in turn, facilitated the generation of ROS, including the hydroxyl radical. It is observed that the reaction of the CP antibiotic with (˙OH) produced the CO2, H2O, and etc.Scheme 1 The photocatalytic pathway of CuPF6/g-CN under VIS light irradiation.

Scheme 1

Scheme 2 Possible passway for the removal of CP under VIS light catalyzed by CuPF6/g-CN.

Scheme 2

A series of control experiments were meticulously conducted to thoroughly investigate the pivotal reactive species involved in the photocatalytic degradation of CP in water by the CuPF6/g-CN catalyst under sunlight. We strategically introduced various radical scavengers into the reaction system to selectively trap different reactive species. 1.0 mmol of KI, AgNO3, ascorbic acid, and t-BuOH were carefully added to the reaction mixture to effectively trap holes (h+), electrons (e−), superoxide radicals (•O2−), and hydroxyl radicals (•OH), respectively. It was observed that the incorporation of ascorbic acid and t-BuOH significantly impacted the degradation reaction rate of CP, while KI and AgNO3 played a relatively diminished role in the photocatalytic activity compared to t-BuOH and ascorbic acid. These findings clearly and conclusively demonstrate that both •O2− and •OH species are essential components in the photocatalytic oxidation process (Fig. 15).Fig. 15 The Impact of radical scavengers on the oxidation yields of CP Catalyzed by CuPF6/g-C3N4.

Fig. 15

4 Conclusions

In summary, the combination of g-CN with Tetrakis(acetonitrile)copper(I) hexafluorophosphate (CuPF6/g-CN) resulted in the development of a highly effective photocatalyst. This photocatalyst exhibited exceptional performance in the removal of CP under VIS light irradiation. In this study, we evaluated the performance of g-CN, CuO/g-CN, [(CH3CN)4Cu]PF6 salt, and CuPF6/g-CN photocatalysts. Among these, CuPF6/g-CN demonstrated superior effectiveness, exhibiting a CP elimination rate six times higher than that of g-CN. The presence of copper in the composite probably caused the reduction of the carrier recombination rate and the enhancement of photocatalytic degradation of CP. This project holds promise in providing an efficient and environmentally friendly technology for antibiotics treatment, utilizing CuPF6/g-CN under VIS light.

CRediT authorship contribution statement

Razieh Nejat: Writing – review & editing, Writing – original draft, Methodology, Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

Financial support of this work by Kosar University of Bojnord, Bojnord is gratefully acknowledged.
==== Refs
References

1 Ayodhya D. Veerabhadram G. Influence of g-C3N4 and g-C3N4 nanosheets supported CuS coupled system with effect of pH on the catalytic activity of 4-NP reduction using NaBH4 Flat. Chem. 14 2019 100088 10.1016/j.flatc.2019.100088
2 Flihh S.M. Ammar S.H. Fabrication and photocatalytic degradation activity of core/shell ZIF-67@ CoWO4@ CoS heterostructure photocatalysts under visible light Environ. Nano. Monit. Manag. 16 2021 100595 10.1016/j.enmm.2021.100595
3 Kareem Y.S. Ammar S.H. Darwash R.A. Microwave-induced catalytic oxidative desulfurization of gasoil fraction over phosphotungstic acid-based magnetic silica (Ni@ SiO2\PWA) nanocatalyst Catal. Commun. 136 2020 105926 10.1016/j.catcom.2020.105926
4 Elaibi A.I. Ammar S.H. Mohammed I.Sh Jabbar Z.H. Construction of heteropolyacid-anchored magnetic g-C3N4/Fe3O4@polyindole hybrids for efficient photocatalytic destruction of methyl orange and bacteria J. Photochem. Photobiol., A 444 2023 114923 10.1016/j.jphotochem.2023.114923
5 Nejat R. Najminejad Z. Fazlali F. Shahraki S. Khazaee Z. g-C3N4/H3PW4Mo8O40 S-scheme photocatalyst with enhanced photocatalytic oxidation of alcohols and sulfides Inorg. Chem. Commun. 132 2021 108842 10.1016/j.inoche.2021.108842
6 Ong W.J. Tan L.L. Chai S.P. Yong S.T. Mohamed A.R. Surface charge modification via protonation of graphitic carbon nitride (g-C3N4) for electrostatic self-assembly construction of 2D/2D reduced graphene oxide (rGO)/g-C3N4 nanostructures toward enhanced photocatalytic reduction of carbon dioxide to methane Nano Energy 13 2015 757 770 10.1016/j.nanoen.2015.03.014
7 Salehnia F. Hosseini M. Ganjali M.R. A fluorometric aptamer based assay for cytochrome C using fluorescent graphitic carbon nitride nanosheets Microchim. Acta 184 2017 2157 2163 10.1007/s00604-017-2130-6
8 Zhao Q. Zhou H. Wu W. Wei X. Jiang Sh Zhou T. Liu D. Lu Q. Sensitive electrochemical detection of tetrabromobisphenol A based on poly(diallyldimethylammonium chloride) modified graphitic carbon nitride-ionic liquid doped carbon paste electrode Electrochim. Acta 254 2017 214 222 10.1016/j.electacta.2017.09.114
9 Shi J. Tai M. Hou J. Qiao Y. Liu C. Zhou T. Wang L. Hu B. Intramolecular D-A structure and n-π* transition co-promoted photodegradation activity of carbon nitride: performance, mechanism and toxicity insight Chem. Eng. J. 456 2023 141029 10.1016/j.cej.2022.141029
10 Wang Y. Zhou T. Wang H. Wang L. Qi J. Cui K. Liu C. Hu B. Fabricating fragmented intramolecular D-A integrated carbon nitride photocatalyts with elevating activity: performance and mechanism analysis Int J Hydrogen Energ 51 2024 61 71 10.1016/j.ijhydene.2023.09.269
11 Zhou T. Che G. Liu C. Ding L. Teng H. Recent advances on small molecule doped carbon nitride photocatalysts: application in environmental water remediation and clean energy production Arab. J. Chem. 17 2024 105808 10.1016/j.arabjc.2024.105808
12 Huang J. Zhang X. Song H. Chen C. Han F. Wen C. Protonated graphitic carbon nitride coated metal-organic frameworks with enhanced visible-light photocatalytic activity for contaminants degradation Appl. Surf. Sci. 441 2018 85 98 10.1016/j.apsusc.2018.02.027
13 Meng, T., Guangbo C., Tianyu, Zhou, Honghui, T., Chunbo, L., Bo, H., 2025. Tailoring C-defect O-doping and n-π* transition awakened porous ultra-thin carbon nitride for efficient peroxymonosulfate activation: Performances and mechanism insight. J. Environ. Sci. 152, 353-367. 10.1016/j.jes.2024.05.012.
14 Fadhil M.H. Ammar S.H. Jabbar M.F.A. Microwave-assisted catalytic oxidative desulfurization of gasoil fuel using synthesized CuO-ZnO nanocomposites J. Fuel Chem. Technol. 47 9 2019 1075 1082 10.1016/S1872-5813(19)30044-1
15 Xu L. Ling S. Li H. Yan P. Xia J. Qiu J. Wang K. Li H. Yuan Sh Photoelectrochemical monitoring of 4-chlorophenol by plasmonic Au/graphitic carbon nitride composites Sens. Actuators B. chem. 240 2017 308 314 10.1016/j.snb.2016.08.038
16 Li C. Wu H. Zhu D. Zhou T. Yan M. Chen G. Sun J. Dai G. Ge F. Dong H. High-efficient charge separation driven directionally by pyridine rings grafted on carbon nitride edge for boosting photocatalytic hydrogen evolution Appl. Catal. B Environ. 297 2021 120433 10.1016/j.apcatb.2021.120433
17 Chen D. Li B. Pu Q. Chen X. Wen G. Li Z. Preparation of Ag-AgVO3/g-C3N4 composite photo-catalyst and degradation characteristics of antibiotics J. Hazard Mater. 373 2019 303 312 10.1016/j.jhazmat.2019.03.090 30925390
18 Huang Sh Xu Y. Xie M. Xu H. He M. Xia J. Huang L. Li H. Synthesis of magnetic CoFe2O4/g-C3N4 composite and its enhancement of photocatalytic ability under visible-light Coll. Surf. A Physicochem. Eng. Asp. 478 2015 71 80 10.1016/j.colsurfa.2015.03.035
19 Fa W. Zan L. Gong C. Zhong J. Deng K. Solid-phase photocatalytic degradation of polystyrene with TiO2 modified by iron (II) phthalocyanine Appl. Catal. B Environ. 79 3 2008 216 223 10.1016/j.apcatb.2007.10.018
20 Guo Z. Chen B. Zhang M. Mu J. Shao C. Liu Y. Zinc phthalocyanine hierarchical nanostructure with hollow interior space: solvent–thermal synthesis and high visible photocatalytic property J. Colloid Interface Sci. 348 1 2010 37 42 10.1016/j.jcis.2010.04.035 20471653
21 Pan G. Sun Z. Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH Chemosphere 283 2021 131257 10.1016/j.chemosphere.2021.131257
22 Yang L. Ren X. Zhang Y. Chen Z. Wan J. One-step synthesis of a heterogeneous catalyst: Cu+-decorated triazine-based g-C3N4 nanosheet formation and catalytic mechanism J. Envir. Chem. Engin. 9 4 2021 105558 10.1016/j.jece.2021.105558
23 Dou X. Chen Y. Shi H. CuBi2O4/BiOBr composites promoted PMS activation for the degradation of tetracycline: S-scheme mechanism boosted Cu2+/Cu+ cycle Chem. Engin. J. 431 2022 134054 10.1016/j.cej.2021.134054
24 Abrishami F. Soufi A. Mahyari M. Cu(I)@g-C3N4/PEI: a new heterogeneous catalyst for Glaser reaction in Deep Eutectic solvent Cata. Let. 2023 2989 3002 10.1007/s10562-022-04188-9
25 Pan G. Sun Z. Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH Chem. Osph. 283 2021 131257 10.1016/j.chemosphere.2021.131257
26 Chen D. Li B. Pu Q. Chen X. Wen G. Li Z. Preparation of Ag-AgVO3/g-C3N4 composite photo-catalyst and degradation characteristics of antibiotics J. Hazard Mater. 373 2019 303 312 10.1016/j.jhazmat.2019.03.090 30925390
27 Davis R. Markham A. Balfour J.A. Ciprofloxacin: an updated review of its pharmacology, therapeutic efficacy and tolerability Drugs 51 6 1996 1019 1074 10.2165/00003495-199651060-00010 8736621
28 Chang X. Yao X. Ding N. Yin X. Zheng Q. Lu S. Shuai D. Sun Y. Photocatalytic degradation of trihalomethanes and haloacetonitriles on graphitic carbon nitride under visible light irradiation Sci. Total Environ. 682 2019 200 207 10.1016/j.scitotenv.2019.05.075 31121346
29 Kamagate M. Assadi A.A. Kone T. Giraudet S. Coulibaly L. Hanna Kh Use of laterite as a sustainable catalyst for removal of fluoroquinolone antibiotics from contaminated water Chem. Osph. 195 2018 847 853 10.1016/j.chemosphere.2017.12.165
30 Hassani A. Khataee A. Karaca S. Photocatalytic degradation of ciprofloxacin by synthesized TiO2 nanoparticles on montmorillonite: effect of operation parameters and artificial neural network modeling J. Mol. Catal. Chem. 409 2015 149 161 10.1016/j.molcata.2015.08.020
31 Fei Y. Li Y. Han Sh Ma J. Adsorptive removal of ciprofloxacin by sodium alginate/graphene oxide composite beads from aqueous solution J. Colloid Interface Sci. 484 2016 196 204 10.1016/j.jcis.2016.08.068 27614043
32 Li L. Liu J. Zeng J. Li J. Liu Y. Sun X. Xu L. Li L. Complete degradation and detoxification of ciprofloxacin by a micro-/nanostructured biogenic Mn oxide composite from a highly active Mn2+-oxidizing pseudomonas strain Nano. Mater. 11 7 2021 1660 10.3390/nano11071660
33 Ye L. Liu J. Jiang Z. Peng T. Zan L. Facets coupling of BiOBr-g-C3N4 composite photocatalyst for enhanced visible-light-driven photocatalytic activity Appl. Catal., B 142 2013 1 7 10.1016/j.apcatb.2013.04.058
34 Kubas G.J. Monzyk B. Crumblis A.L. Tetrakis (acetonitrile) copper (1+) hexafluorophosphate (1‐) Inorg. Synth. 28 1990 68 70 10.1002/9780470132593.ch15
35 Liu J. Zhang T. Wang Z. Dawson G. Chen W. Simple pyrolysis of urea into graphitic carbon nitride with recyclable adsorption and photocatalytic activity J. Mater. Chem. 21 38 2011 14398 14401 10.1039/C1JM12620B
36 Goettmann F. Fischer A. Antonietti M. Thomas A. Chemical synthesis of mesoporous carbon nitrides using hard templates and their use as a metal‐free catalyst for Friedel–Crafts reaction of benzene Angew. Chem., Int. Ed. 45 27 2006 4467 4471 10.1002/anie.200600412
37 Lee S.C. Lintang H.O. Yuliati L. A urea precursor to synthesize carbon nitride with mesoporosity for enhanced activity in the photocatalytic removal of phenol Chem. Asian J. 7 9 2012 2139 2144 10.1002/asia.201200383 22733646
38 Li K. Zeng Z. Yan L. Luo Sh Luo X. Huo M. Guo Y. Fabrication of platinum-deposited carbon nitride nanotubes by a one-step solvothermal treatment strategy and their efficient visible-light photocatalytic activity Appl. Catal., B 165 2015 428 437 10.1016/j.apcatb.2014.10.039
39 Patnaik S. Martha S. Madras G. Parida K. The effect of sulfate pre-treatment to improve the deposition of Au-nanoparticles in a gold-modified sulfated g-C3N4 plasmonic photocatalyst towards visible light induced water reduction reaction Phys. Chem. Chem. Phys. 18 41 2016 28502 28514 10.1039/C6CP04262G 27722288
40 Pan G. Sun Z. Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH Chem. Osph. 283 2021 131257 10.1016/j.chemosphere.2021.131257
41 Kritchenkov I.S. Shakirova J.R. Tunik S.P. Efficient one-pot green synthesis of tetrakis (acetonitrile) copper (I) complex in aqueous media RSC Adv. 9 27 2019 15531 15535 10.1039/C8RA10564B 35514835
42 Sun H. Zhou G. Wang Y. Suvorova A. Wang Sh A new metal-free carbon hybrid for enhanced photocatalysis ACS Appl. Mater. Interfaces 6 19 2014 16745 16754 10.1021/am503820h 25212502
43 Wang X. Maeda K. Thomas A. Takanabe K. Xin G. Carlsson J.M. Domen K. Antonietti M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light Nat. Mater. 8 1 2009 76 80 10.1038/nmat2317 18997776
44 Tuna Ö. Simsek E.B. Synergic contribution of intercalation and electronic modification of g-C3N4 for an efficient visible light-driven catalyst for tetracycline degradation J. Environ. Chem. Eng. 8 5 2020 10.1016/j.jece.2020.104445
45 Guo F. Li M. Ren M. Huang X. Shu K. Shi W. Lu C. Facile bottom-up preparation of Cl-doped porous g-C3N4 nanosheets for enhanced photocatalytic degradation of tetracycline under visible light Sep. Purif. Technol. 228 2019 115770 10.1016/j.seppur.2019.115770
46 Li G. Wang B. Zhang J. Wang R. Liu H. Er-doped g-C3N4 for photodegradation of tetracycline and tylosin: high photocatalytic activity and low leaching toxicity Chem. Eng. J. 391 2020 123500 10.1016/j.cej.2019.123500
47 Bui T.S. Bansal P. Lee B.K. Mahvelati-Shamsabadi T. Soltani T. Facile fabrication of novel Ba-doped g-C3N4 photocatalyst with remarkably enhanced photocatalytic activity towards tetracycline elimination under visible-light irradiation Appl. Surf. Sci. 506 2020 1 12 10.1016/j.apsusc.2019.144184
48 Ren Z. Chen F. Wen K. Lu J. Enhanced photocatalytic activity for tetracyclines degradation with Ag modified g-C3N4 composite under visible light J. Photochem. Photobiol. Chem. 389 2020 112217 10.1016/j.jphotochem.2019.112217
49 Li F. Zhu P. Wang S. Xu X. Zhou Z. Wu C. One-pot construction of Cu and O co-doped porous g-C3N4 with enhanced photocatalytic performance towards the degradation of levofloxacin RSC Adv. 9 2019 20633 20642 10.1039/c9ra02411e 35515531
50 Roca Jalil M.E. Baschini M. Sapag K. Influence of pH and antibiotic solubility on the removal of ciprofloxacin from aqueous media using montmorillonite Appl. Clay Sci. 114 2015 69 76 10.1016/j.clay.2015.05.010
51 Chen D. Ray A.K. Photodegradation kinetics of 4-nitrophenol in TiO2 suspension Water Res. 32 11 1998 3223 3234 10.1016/S0043-1354(98)00118-3
52 Ding Q. Lam F.L.Y. Hu X. Complete degradation of ciprofloxacin over g-C3N4-iron oxide composite via heterogeneous dark Fenton reaction J. Environ. Manage. 244 2019 23 32 10.1016/j.jenvman.2019.05.035 31108307
53 Lin T.Y. Zhu C.Z. Zhang P. Wang Y. Wu H.H. Feng J.J. Zhang J. Regiodivergent intermolecular [3+ 2] cycloadditions of vinyl aziridines and allenes: stereospecific synthesis of chiral pyrrolidines Angew. Chem. 128 36 2016 11002 11006 10.1002/ange.201605530
