SEMICONDUCTOR PHOTOCATALYST AND PREPARATION METHOD THEREOF
20200156053 ยท 2020-05-21
Inventors
- Mohammad Haghighi Parapari (Tabriz, IR)
- Maryam Shabani Mollasaraei (Shaft, IR)
- Amir Haghighi Parapari (Ardebil, IR)
Cpc classification
B01J35/33
PERFORMING OPERATIONS; TRANSPORTING
B01J27/128
PERFORMING OPERATIONS; TRANSPORTING
B01J35/30
PERFORMING OPERATIONS; TRANSPORTING
B01J35/19
PERFORMING OPERATIONS; TRANSPORTING
B01J37/009
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J35/00
PERFORMING OPERATIONS; TRANSPORTING
B01J37/00
PERFORMING OPERATIONS; TRANSPORTING
B01J23/889
PERFORMING OPERATIONS; TRANSPORTING
B01J37/34
PERFORMING OPERATIONS; TRANSPORTING
Abstract
The present invention discloses a novel magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor photocatalyst as a staggered multi-heterojunction nano-photocatalyst for pharmaceutical effluents remediation, and preparation method and use thereof. The semiconductor photocatalysts are at weighted ratios 9:1 4:1, 7:3 and 3:2 of BiOClBi.sub.24O.sub.31Cl.sub.10 and MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor. The BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor photocatalyst with 10% MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 is a solar light activated photocatalyst for pharmaceutical effluents remediation. The pharmaceutical effluents include ofloxacin antibiotic. The mentioned semiconductor photocatalyst effectively removes the ofloxacin (OFL) antibiotic from polluted aqueous solution under simulated solar light, facilitates separation of photocatalyst from treated aqueous solution using magnetic property, enhances light absorption edge, improves intra-particle mass transfer, increases adsorption capacity and promotes efficient surface reactions, which includes: increasing the light absorption range, increasing quantum efficiency and reducing the recombination phenomenon.
Claims
1. A method of preparing a semiconductor photocatalyst, comprising: preparing a mixed phase of MnFe.sub.2O.sub.4Fe.sub.2O.sub.3; and reacting said mixed phase with a BiOClBi.sub.24O.sub.31Cl.sub.10 precursor phase, to form a staggered multi-heterojunction structure of BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (BOC-MFO) semiconductor photocatalyst.
2. The semiconductor photocatalyst of claim 1, is a solar light activated photocatalyst for pharmaceutical effluents remediation.
3. The semiconductor photocatalyst of claim 2, wherein the pharmaceutical effluents include ofloxacin antibiotic.
4. The semiconductor photocatalyst of claim 1, is in a form of composite nanosheets.
5. The semiconductor photocatalyst of claim 1, is of at least one of the weight ratios of 9:14:1, 7:3 or 3:2.
6. The semiconductor photocatalyst of claim 1, is synthesized through sono-solvothermal method.
7. The method of preparing a semiconductor photocatalyst of claim 1, further comprising: a) preparing a mixed phase of MnFe.sub.2O.sub.4Fe.sub.2O.sub.3; b) dispersing a predefined amount of BiOClBi.sub.24O.sub.31Cl.sub.10 precursor phase in a solvent using ultrasound waves; c) dispersing a predefined amount of first mixed phase in a mixture obtained at step (b) using ultrasound waves; d) heating a mixture obtained at step (c) in an autoclave for sono-solvothermal reaction; e) cooling the heated mixture of step (d) at room temperature; f) filtering and washing a precipitate of step (e) using deionized water, and g) drying a mixture of step (f) to obtain BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor photocatalyst.
8. The semiconductor photocatalysts of claim 1, wherein the mixed phase of MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 is prepared during sono-precipitation, aging combined with ultrasound, reflux and calcination steps, respectively.
9. The method of claim 8, wherein the mixed phase of MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 is prepared using a process comprising the steps of: (i) dissolving a stoichiometric quantity of Mn(NO.sub.3).sub.2.4H.sub.2O and Fe(NO.sub.3).sub.3.9H.sub.2O in 400 mL deionized water; (ii) adding a precipitate agent to a mixture of step (i) while subjecting to ultrasonic irradiation. (iii) continuing the addition of the precipitate agent until pH reaches a range of 11-12 for sono-precipitation; (iv) subjecting a mixture of step (iii) to ultrasonic irradiation. (v) refluxing a mixture of step (iv); (vi) filtering and washing a mixture of step (v) using deionized water; (vii) drying a mixture of step (vi), and (viii) calcining the dried mixture of step (vii) to form the mixed phase MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 as intra-heterojunction.
10. The method of claim 9, wherein the precipitate agent is 2M NaOH.
11. The method of claim 9, wherein the ultrasound conditions for sono-precipitation step are: power=200 W; temperature=50-70 C.; and using probe typed ultrasound with frequency at about 20 kHz.
12. The method of claim 9, wherein the reflux conditions are: temperature=100 C.; and time=2 hours.
13. The method of claim 1, wherein the BOC-MFO nanocomposites are prepared using a process comprising the steps of: (i) regarding the weighed ratios of BOC to MFO, the certain amount of BOC precursor was well sonicated in the solvent at a specified power and time; (ii) the appropriate value of as-prepared MFO was added the above suspended mixture with ultrasound assisted dispersion at a specified power and time; (iii) the transfer of the obtained mixture into a Teflon-lined stainless steel autoclave reactor and solvo-thermally heated at the specified temperature and time; and (iv) after natural cooling to the ambient temperature, the precipitate was filtrated, washed by deionized water for several times and dried in an oven at 110 C. for 12 hours.
14. The method of claim 13, wherein step (i) conditions are: the amount of solvent=70 mL; power of sonication=200 W; time of sonication=30 minutes; temperature=25 C.; and using probe typed ultrasound with frequency at about 20 kHz.
15. The method of claim 13, wherein step (ii) conditions are: power of sonication=200 W; time of sonication=1 hour; temperature=25 C.; and using probe typed ultrasound with frequency at about 20 kHz.
16. The method of claim 13, wherein step (iii) conditions are: temperature=150 C.; and time=12 hours.
17. The semiconductor photocatalyst of claim 1, wherein there are the BET surface area and total pore volume more than of 160 m.sup.2/g and 0.5 cm.sup.3/g, respectively.
18. The semiconductor photocatalyst of claim 1, wherein the size distribution of pores is in the range of 2.5-50 nm which has meso-pores into its structure.
19. The semiconductor photocatalyst of claim 1, has the nanosheet morphology, which the average of sheets thickness is at about 19.7 nm.
20. The semiconductor photocatalyst of claim 1, has 99.8% remediation under the conditions as follow: antibiotic concentration: 15 mg/L; semiconductor dosage: 2 mg/L; pH of solution: 3; and under 120 minutes of simulated solar light irradiation
Description
BRIEF DESCRIPTION OF DRAWINGS
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DETAILED DESCRIPTION
[0058] The present invention generally relates to a semiconductor photocatalyst and preparation method thereof. More particularly, the present invention relates to a BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor as a staggered multi-heterojunction nano-photocatalyst for pharmaceutical effluents remediation, and preparation method and use thereof.
[0059] The present disclosure relates to a photocatalyst that could effectively remove the ofloxacin (OFL) antibiotic from polluted aqueous solution under simulated solar light. Further, the disclosure relates to a photocatalyst comprising features, including high activity and stability in the sunlight spectrum; facilitating intra-particle mass transfer (Step 2 of 7 steps in photocatalytic/catalytic processes); increasing surface adsorption phenomenon (Step 3 of 7 steps in photocatalytic/catalytic processes); improving surface reactions namely: increasing the light absorption range, increasing quantum efficiency and reducing the recombination phenomenon (Step 4 of 7 steps in photocatalytic/catalytic processes); facilitating the separation of photocatalyst from treated aqueous solution; and high physico-chemical stability of photocatalyst, leading to more reuse.
[0060] In the context of the present disclosure, in present invention, the target is the design and synthesis of the novel magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposite photocatalyst with 10% MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 to improve the challenges of BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10. In the structure of the novel magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposite photocatalyst, the staggered band gap was formed between BiOClBi.sub.24O.sub.31Cl.sub.10 and MnFe.sub.2O.sub.4Fe.sub.2O.sub.3, which MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 also is as an intra-heterojunction between MnFe.sub.2O.sub.4 and Fe.sub.2O.sub.3 that is an important issue. Generally, with design of a photocatalyst as a magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposite photocatalyst, it could cover the challenges as follow: (i) conformation of its high activity in the sunlight spectrum compared to pure BiOCl; (ii) facilitating intra-particle mass transfer (Step 2 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl; (iii) increasing surface adsorption phenomenon (Step 3 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (iv) improving its surface reactions as increasing the light absorption range, probably increasing quantum efficiency and reducing the recombination phenomenon (Step 4 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (v) conformation of its separation facilitation from treated aqueous solution compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (vi) its good stability after three cycles at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L; and (vii) remediation (adsorption+degradation) obtained: 99.8% in the degradation of a complex and emerging pollutant. So that it can be a more effective perspective to do the future investigation.
[0061] A description of embodiments of the present invention will now be given with reference to the figures. It is expected that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
[0062] The present invention discloses a semiconductor photocatalyst and preparation method thereof. The semiconductor photocatalyst comprises a BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (hereinafter, also referred as BOC-MFO) semiconductor as a staggered multi-heterojunction nano-photocatalyst for pharmaceutical effluents remediation.
[0063] Referring to
[0064] At step 110, a first mixed phase of MFO with intra-heterojunction was prepared using one-pot sono-precipitation, aging combined with ultrasound, reflux and calcination method. This mixed phase is prepared using a process as follows. At step 102, a stoichiometric quantity of Mn(NO.sub.3).sub.2.4H.sub.2O and Fe(NO.sub.3).sub.3.9H.sub.2O are dissolved in a 400 mL of deionized water. At step 104, 2M NaOH solution, as precipitate agent, is gradually added to a mixture of step 102 while subjecting to ultrasonic irradiation at power 200 W until and at temperature range between 50-70 C. using probe typed ultrasound with frequency at about 20 kHz. The addition of the precipitate agent is continued until the pH of the mixture reaches the range of 11-12. At step 106 as aging combined with ultrasound, a mixture of step 104 is subjected to ultrasound assisted dispersion at 200W for 30 min and at temperature range between 50-70 C. using probe typed ultrasound with frequency at about 20 kHz. At step 108 as reflux step, the mixture of step 106 is refluxed at 100 C. for 2 hours to form a precipitate. At step 110, the precipitate is filtrated and washed with deionized water and ethanol for several times. At step 112, the washed mixture is dried in an oven at 110 C. for 6 hours. At step 114 as calcination step, the dried mixture is calcined in a furnace (air ambient) at 1000 C. for 5 hours. At step 116, MFO magnetic nano-photocatalyst is obtained.
[0065] At step 180, the MFO mixed phase and the BOC precursor phase is reacted. At step 182, a certain amount of BOC is well dispersed in the 70 mL ethylene glycol as solvent using ultrasound waves at the power of 200 W for 30 minutes and at temperature 25 C. using probe typed ultrasound with frequency at about 20 kHz. At step 184, an appropriate quantity of MFO is added to a mixture of step 182 with ultrasound assisted dispersion at the power of 200 W for 1 hour and at temperature 25 C. using probe typed ultrasound with frequency at about 20 kHz. At step 186, a mixture obtained at step 184 in an autoclave at 150 C. for 12 h for sono-solvothermal process. At step 188, the heated mixture (precipitate formed and solvent) is cooled at room temperature to reach ambient temperature. At step 190, the cooled precipitate is filtered and washed using deionized water for several times. At step 192, the precipitate of step 190 is dried in an oven at 110 C. for 12 hours to obtain the semiconductor photocatalyst of BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (BOC-MFO), at step 194. In one embodiment, the weighted percentage of BOC-MFO is 10%. In another embodiment, the weighted percentage of BOC-MFO is 20%. In yet another embodiment, the weighted percentage of BOC-MFO is 30%. In yet another embodiment, the weighted percentage of BOC-MFO is 40%.
[0066] The different weighted percentages of BOC-MFO samples are characterized by XRD, FESEM, EDX, BET-BJH, UV-Vis DRS, VSM techniques and pH value at the point of zero charge (pHpzc) to evaluate their photocatalytic performance and determine the optimum sample. The optimum sample is employed in the degradation of ofloxacin (OFL) antibiotic under simulated solar-light to evaluate the influence of various effective factors. In the following, results related to the characterization and rector tests are described.
EXAMPLES
Example 1: XRD Analysis
[0067] Referring to
[0068] For pure MFO (the absence of BOC), the characteristic peaks of the -Fe.sub.2O.sub.3 and MnFe.sub.2O.sub.4 phases was seen, which these results also indicate the formation of a mixed-phase and the creation an intra-heterostructure between two phases of -Fe.sub.2O.sub.3 and MnFe.sub.2O.sub.4.
Example 2: FESEM Analysis
[0069] FESEM (field emission scanning electron microscopy) images (300, 310, 320, 330) of BOC-MFO of 10 wt %, BOC-MFO of 20 wt %, BOC-MFO of 30 wt % and BOC-MFO of 40 wt % samples are displayed in
[0070] Referring to
Example 3: EDX-Dot Mapping Analysis
[0071] Referring to
[0072]
[0073]
Example 4: BET-BJH Analysis
[0074] To estimate the specific surface area, total pore volume, diameter and type of constituent pores of BOC-MOF nano-photocatalyst of 10 wt %, Barrett-Emmett-Teller and Joyner-Halenda (BET-BJH) analysis based on nitrogen adsorption-desorption was conducted, indicating in
[0075] The pore size distribution, which were derived using BJH method from the desorption branch of the isotherm and is shown in graph 650 of
Example 5: DRS Analysis
[0076] In order to evaluate the optical behavior and calculate the band gap of as-synthesized BOC-MFO of 10 wt %, the ultraviolet-visible diffuse reflectance spectra (DRS) from 280 to 700 nm were done, which results is shown in
[0077] This result suggests that the BOC-MFO (10%) nano-photocatalyst can produce electron-hole pairs by absorbing light in the wavelength low than 484 nm. The bang gap is calculated using the DRS analysis and the Kubelka-Munk equation ((h).sup.0.5=A (hvEg)), where , h, , A, E.sub.g are absorption coefficient, Planck constant (4.13567 10-15 eV), light frequency, the constant and band gap energy of photocatalyst, respectively. As depicted in graph 750 of
Example 6: VSM Analysis
[0078] To evaluate the magnetic properties of BOC-MFO (10%) and MFO samples, the VSM analysis (vibrating sample magnetometer) was carried out at the room temperature. Graphs (800, 850) illustrating the results are shown in
Example 7: pHpzc Analysis
[0079] pHpzc (pH value at the point of zero charge), as a surface feature, is an effective parameter to determine the photocatalyst surface charge, which has a noteworthy effect on the adsorption of pollutants and subsequently on the photodegradation efficiency. Referring to
Example 8: Reactor Tests
Evaluation of Photocatalytic Performance:
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TABLE-US-00001 TABLE 1 Molecular Isoelectric Chemical weight constants Therapeutic Chemical structure formula (g/mol) (pKa) max(nm) group
[0081] To estimate and evaluate the heterogeneous photocatalytic ability of nanocomposite fabricated, the photodegradation of ofloxacin (as an antibiotic pollutant which its physicochemical properties is presented in Table 1) into the aqueous solution was performed at the ambient temperature and pressure under a 400 W halogen lamp, as the simulated sunlight source, which emits wavelengths higher to 315 nm.
[0082] The nanocomposite (BOC-MFO (10%), BOC-MFO (20%), BOC-MFO (30%) and BOC-MFO (40%)) of 0.2 g was poured into 200 mL of the aqueous solution, which involved 25 mg/L ofloxacin. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of nanocomposites.
[0083] The BOC-MFO (10%) of 0.4 g was poured into 200 mL of the aqueous solution, which involved 25 mg/L ofloxacin with pH=6. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0084] The BOC-MFO (10%) of 1 g was poured into 200 mL of the aqueous solution, which involved 25 mg/L ofloxacin with pH=6. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0085] The BOC-MFO (10%) of 0.2 g was poured into 200 mL of the aqueous solution, which involved 15 mg/L ofloxacin with pH=6. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0086] The BOC-MFO (10%) of 0.2 g was poured into 200 mL of the aqueous solution, which involved 35 mg/L ofloxacin with pH=6. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0087] The BOC-MFO (10%) of 0.2 g was poured into 200 mL of the aqueous solution, which involved 25 mg/L ofloxacin with pH=3. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0088] The BOC-MFO (10%) of 0.2 g was poured into 200 mL of the aqueous solution, which involved 25 mg/L ofloxacin with pH=9. This mixture was placed in the dark surroundings for 30 min while the mixture was stirred magnetically to reach adsorption/desorption equilibration between ofloxacin molecules and the surface of BOC-MFO (10%).
[0089] Afterward, the lamp was turned on and the reactor was exposed to the irradiation of the light source for 120 min. In during of the remediation process, 5 mL of suspension was sampled in the intervals of 15 min. Then, the taken sample was centrifuged to deposit the nano-photocatalyst. In order to monitor the pollutant concentration, UV-Vis spectrophotometer was used and the measurement was done at the 287 nm. The efficiency of heterogeneous photo-degradation was computed using E %=(1C/C.sub.0)*100 equation, that C.sub.0 is belonged to the initial concentration of the pollutant after reaching the adsorption equilibrium; C is belonged to the concentration at the time t.
[0090] Referring to a graph 1000 of
[0091] According to results related to various analyses, this sample appears to be the selected photocatalyst among the magnetic nanocomposites. The reason of the increasing performance of the degradation process by referred sample could be ascribed to the effective formation of a heterojunction between MFO and BOC phases. This hetero-structure can increase the light absorption, accelerate the separation of charge carriers and reduce their recombination. Moreover, the use of ultrasonic waves resulted in a uniform distribution of particles, as the number of available sites increased.
Example 9: Influence of Photocatalyst Loading
[0092]
[0093] Therefore, the percentage of degradation increases. However, increasing the loading to more than 2 g/L leads to the increasing opacity, resulting in the light scattering and light refraction. The light refraction and light scattering cause that the amount of energy associated with h which reaches to the photocatalyst surface reduces. Thus, the number of charge carriers will be reduced. Additionally, there also is the possibility of reducing the number of active sites owing to the agglomeration of nanoparticles or clusters. The events mentioned can decrease the degradation efficiency.
Example 10: Influence of Initial pH
[0094] The pH of solution plays a decisive role in the efficiency of the photocatalytic degradation of organic pollutants, as an advanced oxidation process, especially about antibiotics due to the existence of two isoelectric constants. In order to evaluate the influence of pH on the degradation performance of ofloxacin, experiments were conducted at the pH=3, 6 and 9 that are given in a graph 1200 of
[0095] The consumption of electrons can be further reduced the recombination rate of photoinduced electrons and holes on the surface. Therefore, there are more holes, as the most crucial active specie to destroy ofloxacin. In contrast, in the high pH media (such as pH=9) the surface charge of the BOC-MFO (10%) is negative and ofloxacin also ionizes as an anion considering to the pKa1=8.28. Since the present partial negative charges on the surface of BOC-MFO (10%) and present OH.sup. ions in the solution have the high affinity with holes, so the role of this active specie diminishes extremely, leading to the decrease of degradation efficiency of ofloxacin. It is worth noting, in the pH=6, the occurrence of this event is far less and besides, the adsorption content of ofloxacin on the surface will also increase, considering the charges of photocatalyst surface and ofloxacin molecule.
Example 11: Effect of Initial Concentration
[0096] Another affecting parameter on the efficiency of the photocatalytic process is the initial concentration of the pollutant.
[0097] Therefore, the generation of reactive oxygen species will decrease because of the many active sites occupied by pollutant molecules. In addition, the increment of ofloxacin concentration causes to that the light irradiated with same initial energy don't reach the surface of photocatalyst due to the absorption of light by the contaminant molecules adsorbed on the surface. There may also be a competitive state between the intermediate molecules formed by the photodecomposition of ofloxacin and the contaminant molecules, which will also reduce the process efficiency.
[0098] In general, according to the above mentioned descriptions, it can be stated the following items for BOC-MFO (10%) nanocomposite: (i) for conditions, where the catalyst loading is 1 g/L, initial concentration is 15 mg/L and initial pH is 6, the degradation percentage was obtained 82.5%; (ii) for conditions, where the catalyst loading is 2 g/L, initial concentration is 25 mg/L and initial pH is 6, the degradation percentage was obtained 82.4%; and (iii) for conditions, where the catalyst loading is 1 g/L, initial concentration is 25 mg/L and initial pH is 3, the degradation percentage was obtained 88.2%.
[0099] Consequences depict that at concentrations of about 15 mg/L, loading values of about 2 g/L and at acidic pH, the possibility to achieve high efficiency is provided. These results indicate the successful performance of this nano-photocatalyst. This despite the fact that Bhatia and coworkers (Bhatia et al., 2016) were reported 86% removal for aqueous solution containing 25 mg/L ofloxacin with pH=3, 1.5 g/L of catalyst loading and after 6 hours (360 minutes). The photocatalyst applied in this research was TiO.sub.2 doped with BiNi. As observed, in present invention the operating conditions, especially reaction time, using the BOC-MFO (10%) was greatly improved owing to the consideration of effective factors in its design.
Example 12: Reusability Study
[0100] As shown in a graph 1400 of
Example 13: Suggested Reaction Pathway
[0101] The suggested reaction mechanism for the degradation of ofloxacin antibiotic, as a refractory and complex model pollutant, over BOC-MFO (10%) is represented 1500 in
ECBM=XEe0.5Eg
EVBM=ECBM+Eg
[0102] In these equations, X, Ee, Eg represent the electronegativity of the photocatalyst, energy of free electrons on the hydrogen scale (4.5 eV) and band gap energy, respectively. With respect to the above equations, the ECBM calculated for BOC and MFO nano-photocatalyst were +0.7 and +0.15 eV, respectively and calculated EVBM were about +3.40 and +2.50 eV, respectively. Experience has shown that the placement position of energy levels and the formation of staggered heterojunction are caused to improving the separation of the charge carriers. In other words, the existing electrons of the valence band both of two photocatalysts are transferred to their conduction band and holes remain in their valence band under simulated solar-light.
[0103] Since the conduction band in MFO is more negative than BOC, so, photogenerated electrons on the conduction band layers of MFO can migrate to the conduction band layers of BOC. Moreover, because the energy of the existing holes in the valance band layers of BOC is more, thus, these holes could migrate to the MFO valance band layers. This state reduces the recombination rate of the electron-hole pairs. Additionally, there is an intra-heterojunction between BiOCl and Bi.sub.24O.sub.31Cl.sub.10 in the structure of BOC and an intra-heterojunction between Fe.sub.2O.sub.3 and MnFe.sub.2O.sub.4 in the structure of MFO that could be further reduced the recombination phenomena related to charge carriers.
[0104] Therefore, a staggered multi-heterojunction is formed in the structure of BOC-MFO (10%) nanocomposite according to the quantum perspective. It is worth noting that since in present invention, the maximum energy emitted from light source was about 315 nm (3.9 eV), so electrons from valence band of BOC and MFO can excite to the level of energy in the conduction band of BOC and MFO with potential energy at about 0.54 eV and 1.41 eV, respectively. Thus, electrons migrated from the conduction layers of the MFO to the BOC conduction layers.
[0105] In view of the redox potential of O.sub.2/.O.sub.2.sup. (0.33 eV), it is possible to produce superoxide radicals by more negative energy levels. Finally, the produced radicals and holes can react with the ofloxacin molecules and generate the degradation products. According to above statements, the following reactions could be proposed for removal of pollutant:
BOC+h.fwdarw.BOC*(e.sup.+h.sup.+)
MFO+h.fwdarw.MFO*(e.sup.+h.sup.+)
e.sup.(MFO)*.fwdarw.e.sup.(BOC)*
h.sup.+(BOC)*.fwdarw.h.sup.+(MFO)*
O.sub.2+e.sup..fwdarw..O.sub.2.sup.
.O.sub.2.sup.+Ofloxacin.fwdarw.Degradation Products.
h.sup.++Ofloxacin.fwdarw.Degradation Products.
Example 14: Kinetic Evaluation
[0106] To evaluate the kinetic rates of the ofloxacin photodegradation on the as-synthesized nanocomposites, pseudo-first-order kinetic pattern (as ln(C/C0) vs. kt) was used, that the experiments outcomes are expressed in graphs (1600, 1650) of
[0107] Advantages of the present invention is disclosed as follows: (i) with design of a photocatalyst as a magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposite photocatalyst with 10% MFO, it could cover the challenges as follow: conformation of its high activity in the sunlight spectrum compared to pure BiOCl; facilitating intra-particle mass transfer (Step 2 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl; increasing surface adsorption phenomenon (Step 3 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; Improving its surface reactions as increasing the light absorption range, probably increasing quantum efficiency and reducing the recombination phenomenon (Step 4 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; conformation of its separation facilitation from treated aqueous solution compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; its good stability after three cycles at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L; and remediation (adsorption+degradation) obtained: 99.8% in the degradation of a complex and emerging pollutant. So that it can be a more effective perspective to do the future investigation; (ii) the precursors used for the fabrication of the BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposites are in-expensive, readily available, and non-toxic, which are important parameters in the synthesis and production of a material; (iii) the sono-solvothermal employed to fabricate the magnetic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposites are: simple, suitable temperature and time conditions which are controllable, the possibility of effective mixing and dispersing between precursors and the creation of a homogeneous solution and the ability to produce controllable morphologies; (iv) the BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 nanocomposite with 10% MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 has a good activity and stability; (v) development and improvement of technical knowledge in order to design and achieve the active photocatalysts in the solar region, which the factors, such as surface reactions, surface adsorption and separation, have been improved; (vi) treatment of water polluted to the resistant organic contaminants, such as antibiotics. The antibiotics are resistant and persistent. Moreover, they can cause toxicity in the environment. Additionally, they can lead to the degradation of microbial population that exists in the soil and water, causing the immunity of microorganisms, which this event leads to the mutation and produce of the more resistant species of bacteria and microbes; and (vii) treatment of water polluted to the resistant organic contaminants using an environmentally friendly and not-expensive method that could operate at the ambient temperature and pressure.
[0108] BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor as a magnetic staggered multi-heterojunction structure and a solar light activated nano-photocatalyst for the remediation of pharmaceutical effluents (such as ofloxacin antibiotic) was successfully synthesized via solvothermal method combined with the ultrasonic irradiance (denoted as: sono-solvothermal). This structure leads to the increment of the light absorption range, facilitation of mass transfer, increasing surface adsorption of contaminant molecules and increasing the efficacious separation and transmission of photoinduced charge carriers, resulting in a reduction of the excitons recombination rate. So, the process efficiency will be increased. Furthermore, due to the magnetic property created, the possibility to separate easily the photocatalyst from treated pharmaceutical effluent is provided.
[0109] In this invention, the photocatalytic degradation of ofloxacin (fluoroquinolone antibiotic and as an emerging contaminant and as a model pollutant with high resistance and complex structure) was investigated to evaluate the performance of nano-photocatalyst synthesized. In other terms, the highlighted advantages are: (a) sono-solvothermal synthesis of the novel BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductor, as staggered multi-heterojunction and solar light activated nano-photocatalyst, in line with the above-mentioned design parameters namely with high activity in the sunlight spectrum, facilitating intra-particle mass transfer, increasing surface adsorption phenomenon, improving its surface reactions as increasing the light absorption range, probably increasing quantum efficiency and reducing the recombination phenomenon, separation facilitation from treated aqueous solution; (b) evaluation of various contents of MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 and the determination of optimum weighted percentage; (c) synthesis of meso-structure staggered multi-heterojunction nanocomposite, which has been had the appropriate specific surface area and pore volume. It is worth noting, organic pollutants are the coarse molecules, so the existence of mesoporous could cause to facilitate the diffusion of organic molecules; (d) synthesis of staggered multi-heterojunction BiOClBi.sub.24O.sub.31Cl.sub.10 (90%)/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%) nanocomposite with appropriate saturation magnetization to facilitate the separation process; (e) highest degradation efficiency over BiOClBi.sub.24O.sub.31Cl.sub.10 (90%)/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%) namely: remediation (adsorption+degradation) at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L was obtained 99.8% in the degradation of ofloxacin as complex and emerging pollutant; (f) increase of reaction rate upon over BiOClBi.sub.24O.sub.31Cl.sub.10 (90%)/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%); (g) efficacious degradation of fluoroquinolone antibiotic under sunlight irradiation; (h) higher spectrum response and the effective separation of charge carriers; (j) good stability after three cycles at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L for BiOClBi.sub.24O.sub.31Cl.sub.10 (90%)/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%); (k) evaluation of the operating parameters influence (such as pollutant concentration, loading and the initial pH of solution) on the process efficiency; (i) discussion of photodegradation mechanism over BiOClBi.sub.24O.sub.31Cl.sub.10 (90%)/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%).
[0110] Moreover, BOC-MFO with 10% MFO is non-toxic and has magnetic property. Besides, it is active in the sunlight spectrum and has the nanosheet morphology, which the thickness of the sheets constituent is about 19.7 nm. This nano-photocatalyst has the high BET surface area and pore volume and the pores constituent are at mesoporous category. Additionally, due to intra-heterojunction and staggered heterojunction between the existing phases, the lifetime of charge carriers increases; Besides the BOC-MFO with 10% MFO has a good performance at determined conditions and the relatively short time for the degradation of ofloxacin antibiotic (as an emerging contaminant and complex) under simulated solar light. It is also easily separated from treated effluents.
[0111] The main challenges for photocatalysis process and the features/method of the present invention to overcome the challenges are discussed as follows. Generally, the main challenges for photocatalysis process could be divided into five general items: (i) low efficiency relevant to surface reactions (such as low photocatalyst activity in the sunlight region and high rate of electron-hole pair recombination); (ii) resistance to intra-particle diffusion; (iii) low adsorption capacity; (iv) low stability; (v) separation issue.
[0112] Regarding to the mentioned challenges, in this invention, the BiOClBiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%) semiconductor with considering effective factors from engineering perspective was synthesized with the following features: (i) considering XRD patterns, the presence of four phases related to BiOCl, Bi.sub.24O.sub.31Cl.sub.10, MnFe.sub.2O.sub.4 and Fe.sub.2O.sub.3 in the structure of the mentioned novel nanocomposite is proved; (ii) considering DRS analysis, there is two absorption edges at 466 and 484 nm, which will improve the surface reactions (Step 4 of 7 steps in photocatalytic/catalytic processes); (iii) considering BET-BJH analysis, the surface area and total pore volume are obtained more than 160 m.sup.2/g and 0.5 cm.sup.3/g, respectively. Moreover, using this analysis, the mesoporous structure of mentioned nanocomposite is proved. This structure is more useful for the diffusion of coarse molecules such as ofloxacin. In other words, considering BET-BJH analysis, the intra-particle mass transfer (Step 2 of 7 steps in photocatalytic/catalytic processes) is facilitate and the surface adsorption phenomenon (Step 3 of 7 steps in photocatalytic/catalytic processes) is increased; (iv) considering FESEM analysis, the thickness of the sheets constituent is about 19.7 nm. This morphology could be enhanced the light penetration with energy emitted and facilitated the available to the active sites.
[0113] (v) considering XRD patterns and DRS analysis, it is as a staggered multi-heterojunction structure and a solar light activated nano-photocatalyst; (vi) considering the type-II formed from the quantum perspective, the separation of charge carriers could be effectively occurred; (vii) considering VSM analysis, it has the saturation magnetization up to 2 emu/g which could facilitate the separation issue; (viii) using this nanocomposite, the reaction rate obeys from pseudo-first-order kinetic model. the appeared constant of this nanocomposite is obtained about 0.0158 min.sup.1; (x) using this nanocomposite, the relatively short reaction time will be needed for the removal of ofloxacin antibiotic, and the occurrence of surface reactions is enhanced; (xi) it has the ability of the efficacious degradation of colorless organic pollutants under sunlight irradiation and displays a good stability after three cycles. So that it can be a more effective perspective to do the future investigation.
[0114] BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 semiconductors with weighted ratios 9:1 4:1, 7:3 and 3:2 were synthesized via sono-solvothermal method and employed in the photocatalytic degradation of antibiotic ofloxacin (OFL) from the polluted aqueous solution under simulated solar light. The results revealed that the BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 magnetic nanocomposite with mass ratio 9 to 1 (abbreviation: BOC-MFO (10%)), which has the nanosheet morphology and mesoporous in its structure, demonstrated 82.5% efficiency after 120 min illumination for 15 mg/L ofloxacin with initial pH=6 and loading 1 g/L. Moreover, remediation (adsorption+degradation) at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L was obtained 99.8% in the degradation of OFL. The photocatalyst efficiency was changed with changing pH, photocatalyst loading and initial concentration of pollutant.
[0115] According to the present invention, commercial applications of the present invention are disclosed. Generally, photocatalysts have many applications in many fields that some of them are: environmental remediation, conversion of harmful gases, renewable energies (solar energy absorption and hydrogen production) and polymerization of various compounds. Regarding the environmental challenges related to water pollutions and the high importance of its remediation, this invention could be used in the post-treatment part of the hospital wastewater, pharmaceutical industries, urban wastewater treatment systems, water treatment, textile industries and etc.
[0116] Water pollution is one of the major environmental problems today, so its remediation is one of the global priorities. However, existing treatment methods such as biological methods cannot remove resistant organic pollutants such as antibiotics. But, the photocatalytic process as an environmentally friendly and low-cost technique can be prominent. In this technique, unlike other conventional technologies, only the use of photocatalysts and light can remove resistant and emerging organic contaminants such as antibiotics that are resistant to conventional treatment methods. Currently, the water and wastewater treatment, water purification process and post-treatment of effluents using photocatalysis process is in the early stages of the commercialization. The process of industrialization of photocatalysts depends on factors such as increasing their ability to absorb sunlight, enhancing their photocatalytic activity, and facilitating their separation from treated solutions.
[0117] In this regard, parameters such as simplicity and cost-effectiveness of the synthesis method, facilitation of intra-particle diffusion phenomena, increasing adsorption capacity, the occurrence of appropriate surface reactions and the facilitation of separation of catalysts at the end treatment process are the factors that are created the challenges of photocatalysis and should be considered in the photocatalyst design, so that researches are still continued in this field. In present invention, photocatalytic BiOClBi.sub.24O.sub.31Cl.sub.10/MnFe.sub.2O.sub.4Fe.sub.2O.sub.3 (10%) nanocomposite, as a staggered heterojunction structure was successfully synthesized using sono-solvothermal. This nanocomposite with nanosheet morphology increases the light absorption range and lifetime of charge carriers produced due to intra-heterojunction and staggered heterojunction between the existing phases. Besides, due to its high specific surface area and pore volume and the existing mesoporous, mass transfer, adsorption and subsequently, photocatalytic degradation of the contaminant molecules are improved. Moreover, the nanocomposite of the present invention could be easily separated from the treated aqueous solution owing to its magnetic property.
[0118] Generally, with design the magnetic BOC-MFO with 10% MFO nanocomposite photocatalyst, it could cover the challenges as follow: (i) conformation of its high activity in the sunlight spectrum compared to pure BiOCl; (ii) facilitating intra-particle mass transfer (Step 2 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl; (iii) increasing surface adsorption phenomenon (Step 3 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (iv) improving its surface reactions as increasing the light absorption range, probably increasing quantum efficiency and reducing the recombination phenomenon (Step 4 of 7 steps in photocatalytic/catalytic processes) compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (v) conformation of its separation facilitation from treated aqueous solution compared to pure BiOCl and BiOClBi.sub.24O.sub.31Cl.sub.10; (vi) its good stability after three cycles at pH=3, catalyst loading=2 g/L and pollutant concentration=15 mg/L; and (vii) remediation (adsorption+degradation) obtained: 99.8% in the degradation of a complex and emerging pollutant. So that it can be a more effective perspective to do the future investigation.
[0119] The foregoing descriptions comprise illustrative embodiments of the present invention. Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only, and that various other alternatives, adaptations, and modifications may be made within the scope of the present invention. Merely listing or numbering the steps of a method in a certain order does not constitute any limitation on the order of the steps of that method.
[0120] Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions. Although specific terms may be employed herein, they are used only in generic and descriptive sense and not for purposes of limitation. Accordingly, the present invention is not limited to the specific embodiments illustrated herein. While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description and the examples should not be taken as limiting the scope of the invention, which is defined by the appended claims.