Submitted:
13 July 2024
Posted:
16 July 2024
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Abstract
The large energy band gap associated with titanium oxide nanoparticle is a limitation to its application as a photo catalyst within the solar spectrum. More than 45% of solar radiation can be utilized at a reduced energy band gap of 〖TiO〗_2. Various structural modifications in 〖TiO〗_2 targeted in optimized photo catalyst application include the enhancement of its support system. Activated carbon supported 〖TiO〗_2 nanoparticle may produce the desired reduction in the energy band gap, reduce electron recombination and consequently enhance its photocatalytic activity in the visible region of electromagnetic spectrum. In the current investigation, an activated carbon made from the leaves of an invasive plant (Acacia Saligna) was applied as a support in the synthesis (hydrothermal process) of 〖TiO〗_2 nanoparticle. The determination of energy band-gap of 〖TiO〗_2 supported activated carbon using UV-Vis spectrophotometer gave 2.11 eV. Likewise, Scanning Electron Microscopy (SEM-EDS), Fourier transformer infrared (FTIR), XRD and Brunauer- Emmett-Teller (BET) showed that 〖TiO〗_2was successfully immobilized on the activated carbon’s external surface. The BET results showed that the synthesized 〖TiO〗_2exhibits small hysteresis phenomenon which represent a typical type IV isotherm attributed to mesosoporous material with a low porosity. Meanwhile, these XRD results reveal the presence of mixture of rutile and anatase crystalline phase
Keywords:
photocatalyst
; titanium (IV) oxide
; biochar
; degradation
; orange II sodium dye
; synthesis
Introduction
Heterogeneous photocatalyst are extensively used for wastewater treatment because of its higher effectiveness in the removal of recalcitrant pollutants and harmful bacteria during the UV-Solar irradiation [1]. The process is based on the photo-activation of semiconductor nanoparticles (TiO₂, SiO₂, Al₂O₃, ZnS) through visible light irradiation. The photo-catalytic oxidation lead to the generation of reactive oxidizing species (commonly OH radical) which can cause the degradation of organic pollutants and denaturation of microbes [2]. The photo-activation of nanomaterials is the transition at ambient temperature of an electron (e−) from the valence band (VB) to the conduction band (CB) due to the absorption of photons having equal or higher energy than the bandgap energy [3]. This absorption generates oxidizing sites known as holes (h+) in the valence band that may react directly with the pollutants. This process can lead to the total degradation of toxic pollutants to harmless species such as carbon dioxide and water [4]. The mechanism of photocatalytic activation in the TiO₂ was as demonstrate [5].
Figure 1.
Schematic illustration of photo-catalytic activation in the TiO2 on removal of pollutants.
Figure 1.
Schematic illustration of photo-catalytic activation in the TiO2 on removal of pollutants.
Titanium dioxide, TiO₂ is the ideal semi-conductor nanoparticle used in the photo-catalytic processes due to its thermochemical stability, cost effectiveness, availability, high reactivity under light irradiation and low toxicity [6]. The high chemical stability of TiO₂ is one of its major advantages over other common heterogenous photocatalysts [7]. However, TiO₂ shows photo-physical limitations due to its large energy bandgap (3.0 - 3.20 eV) which limits its activity to only the UV range (5%) of electromagnetic spectrum [8]. Reductions in the energy band gap of TiO₂ will facilitate its application as a photo-catalyst and enhances the photo-physical utilization of larger percentage of natural solar light. This can be achieved by modifying the TiO₂ with compounds such as metal and non-metal [9].
Titanium (IV) Oxide (Tio2) Modifications of Enhanced Solar Activities
The principal objective of TiO₂ modifications is to reduce its energy bandgap thus moving its optical response from the UV to the visible region and reducing the electron-hole pair recombination. Several modifications techniques including doping with metals and non-metals, dye sensitization, deposition with noble metals, and coupled semiconductor have been applied. However, studies show that doping has a positive effect on TiO₂ because it introduces elements such as metal and non-metal in the titania structure that lead to the increase of its photo-activity by changing the functional properties of the TiO₂ [10,11]. The impact of doping in the photo-catalytic is regulated by factors, such as the nature of the dopants, the synthesis process, and physicochemical properties of the photo-catalyst [2,12].
Metal-Ion Doping
The modification of TiO₂ with metal-ion (transition metals) such as Pt, Au, Ag, Cu, V, Ni and Sn have been discovered to increase the photo-response and photo-catalytic activity of TiO₂ into the visible-light region (Shuying et al., 2015). Metal-ion doping can leads to the duplication of the condoction band (CB) in TiO₂ by the d-orbital of the transition metal, leading to the decrease on the energy band gap [13]. The newly created energy levels between the valence band (VB) and conduction band (CB) ensure the transfer of electrons in the visible light regions of electro-magnetic spectrum [14]. The metal-ion may crosses the optimum limit at a very low concentration and acts as recombination centres for charge carriers by causing the photo-activity. The existence of an acceptable quantity of metal-ion doping (optimum limit) guarantees that the metal particles simply appear as electron traps thus helping electrons-holes split [15]. The transition metal ions can also play the role of recombination sites for the photo-induced charge carriers, therefore, decreasing the quantum effectiveness [13,16]. Besides, metal-ion doping may enhance the rate of electrons/holes recombination and generate thermal imbalance. It is then essential to prevent this by considering the effective quantity of the metal-ion during the synthesis of the doped TiO₂ nanoparticles. Doping with more than one metal oxide such as SiO₂, ZrO₂, WO₃, Fe₂O₃, SnO₂, Ln₂O₃, RuO₂ may invariably lead to the enhancing of TiO2 photocatalytic effectiveness and inducing the diminishing of the bandgap by causing a structure modification into the TiO2. [17]. Therefore, the photo-catalytic activity is increased and the metal oxides expand the TiO₂ surface. The electron-hole pair recombination may also arise as a consequence thermodynamic imbalance in some metal-oxide (RuO₂/TiO₂) [13].
Non-Metal Doping
TiO₂ supported non-metal (such as C, F, B, S, Cl, N, and Br) had been considered as a second-generation photo-catalysts. Doping with non-metal has been widely investigated due to their relatively high photo-stability and TiO₂ structural modification advantages [18]. The main goals of the non-metal doped TiO₂ is to decrease the recombination of electron-hole pairs [19]. Usually, it involve oxygen atoms substitution by the non-metal in the TiO₂ lattice, for a targeted decrease in the band-gap and electron recombination prevention [20]. Notably, non-metal doping at the atomic level can maintain the intrinsic surface properties of the TiO₂, as the dopant act as an isolated particle instead of clusters throughout the surface [18]. Moreover, the exceptional distribution of dopant states is usually found nearly over the VB maximum, making the photo-generated holes on these states oxidative enough for further photo-reactions.
Titanium-Oxide Supported Carbon Composites in Photocatalysis
Extensive studies have been done on the photocatalytic activity of TiO₂ supported carbon in the degradation of organic pollutants [21,22,23]. Singh et al., (2016) studied the degradation of Direct Blue 199 dye using activated carbon-based TiO₂ nanocomposites under 196 W mini lamps. They also studied the reaction kinetic modeling of the photocatalytic, sonocatalytic, and sono-photocatalytic processes. Their result showed that the sono-photocatalytic process showed maximum degradation. However photocatalytic reactor was more efficient as it consumed less energy. They also demonstrated that the degradation reactions of Direct blue 199 followed the Langmuir–Hinshelwood model. Rashed et al., (2017) studied the adsorption and photocatalysis of methyl orange and Cd removal from wastewater using TiO₂/sewage sludge-based activated carbon nanocomposites under (15 W) UV irradiation lamps. They also investigated the factors influencing photocatalysis such as amount of TiO₂, initial pollutant concentrations, solution pH, nanocomposite dosage, and UV irradiation time. Their results revealed that these factors have a direct effect on photocatalysis efficiency. Nguyen et al., (2020) studied the kinetics of adsorption and photocatalysis in the removal of phenol, naphthol blue-black, and reactive black 5 under UV lamps. Their kinetic analysis revealed that the adsorption-assisted photocatalysis performance depended on the similarity of the initial rates of adsorption and degradation determined by the properties of the photocatalyst and the dye. Mondol et al., (2021) synthesised Activated Carbon/ TiO₂ nanohybrids by hydrothermal technique. They studied the photocatalytic activity by photodegradation of Reactive Red-35 dye using solar irradiation in open-air. Their report showed that the photodegradation was mainly controlled by the radicals •OH and •O₂‾. The photo-catalytic performance was significant due to the synergistic effect of adsorption and photodegradation activity of the nanohybrids. Despite the research effort in the synthesis of Activated Carbon/TiO₂ nanocomposite, there are challenges in the preparation process time-line, calcination temperatures and chemical reagents. Therefore, there is a need to apply energy efficient and simple preparation method which will ensure fast production process and depend on cost effective and low energy. Hydrothermal synthesis is a well-known for its tremendous advantages. It has potential for reduced in-process reduction and continuous catalyst activation as well as potential for industrial-scale production. It is also important to consider the sources and economic advantages when chosen the carbon material for the production of bio-char. The various sources of carbon have been investigated for their benefits in the biochar production. However, most trials have supported the use end-of-life biomass (ELB) such as sewage sludge, animal manure and agricultural residues as a feedstock [27]. The use invasive plants can play an important role in reduction of carbon sequestration and unprofitable application of weedicide. The fast production and strong environmental adaptability of invasive plants make them harmful to the environment. Valorisation of this lant therefore aid their control and management.
Port Jackson Willow (Acacia saligna)
The Port Jackson willow (PJ) is a flexible tree that grows rapidly in semi-desert regions (including South Africa) as windscreens and as an ornamental tree. It has become an invasive species outside of its natural range, threatening biological diversity and categorized as an Invasive Alien Plant (IAP) [27]. IAP has a negative impact on the ecosystem by consuming more water than local plants, exhausting valuable water resources, and also providing material for wildfires, making them exceptionally hot, which destroys the soil structure and sterilise the soil for up to three years . This results into negatives ecological, social, and economic impacts.
Chemical Reagents and Materials
The chemical used in the current investigations include; Hydrochloric acid (≥ 37 %), Nitric acid (65 %), ethanol (≥ 99 %), Titanium (III) trichoride solution (≥ 12%), and orange II sodium salt (≥ 85 %). They were purchased from Sigma Aldrich. Port Jackson Willow leaves were obtained from the Cape flats forest and identified at the Department of Botany, University of Cape Town.
Preparation of Biochar
Biochar was prepared by pyrolysis of the port Jackson willow leaves. The collected leaves were washed several times with deionized water to remove dust and other impurities, then dried and grinded into powder form. The 10.0 g of the dried powdered leaves were put in a Teflon crucible and place in the oven at 250 oC for 2 hours (with limited air supply) obtain biochar.
Synthesis of the Photocatalyst
Titanium dioxide TiO₂ was prepared using TiCl₃ precursor. Firstly, TiCl₃ (7 ml) was added to 1.5 ml HCl and mixture was diluted in distilled water (9 ml) and stirred for 15 minutes. The obtained solution was put in a water bath at 80°C for 10 minutes before slowly adding 6 ml of concentrated HNO₃ as the reaction is highly exothermic. The heating was then continued for 10 hours. The resultant titanium solution was washed with deionized water and recovered through centrifugation.
Synthesis of Biochar Supported-TiO2 Nanocomposite
TiO2 supported biochar nanoparticles were obtained by mixing the 200 mg synthesised TiO2 with 50 mg biochar and dissolve the mixture in ethanol (10 ml). The mixture was then sonicated for about 1 hour at room temperature. The solution was dried in the oven for 2 hours at 80oC. The resulting samples were calcinated under N2 stream at 500oC for 3 hours. The obtained powder was washed 50 mL ethanol (30%) and dried in a desiccator. The procedure was repeated at varied ratio of biochar to TiO2 (2:1, 2:2, 2:3 and 2:4).
TAUC Method for Energy Band Gap Determination
Energy band gap of a semiconductor is the needed energy for the excitement of its electron to move from the valence band to the conduction band. This is important in predicting photophysical and photochemical properties of semiconductors. The method is based on the assumption that the energy-dependent absorption coefficient.
Table 1.
The Energy bandgap of the synthesized TiO2 as calculated from TAUC plots.
| Weight TiO₂ (mg) | Weight biochar (mg) | Ratio | Energy band gap(eV) |
|---|---|---|---|
| 200 | 50 | 4 : 1 | 2.52 |
| 200 | 100 | 2 : 1 | 2.50 |
| 200 | 200 | 1 : 1 | 2.49 |
| 200 | 300 | 2 : 3 | 1.96 |
| 200 | 400 | 1 : 2 | 2.12 |
| 200 | 500 | 2 : 5 | 2.33 |
It was discovered that Biochar/ TiO2 (2:3) ratio gave the smallest Energy band gap (1.96 eV). This ratio Biochar/ TiO2 was considered as the optimum for the synthesis of Biochar Supported-TiO2 photocatalyst and it was used for further characterizations and application.
Characterisation of Biochar Obtained from PJW Leaf
The obtained yield of Biochar after the carbonization of the PJW leafs is as presented in Table 2. Increased pyrolysis period (from 1 to 3 hours) lead the reduction in Biochar yield from 70.58 to 68.90 %. The declined yield of biochar at an increased temperature may be attributed to combustion of the retained organic materials and the elimination of retained volatile organic compounds.
Functional Group Identification
The Fourier transform infrared (FT-IR) spectra of the PJW leafs and the prepared Biochar is as presented in Figure 2. The band at 3296 cm-¹ is attributed to the –OH stretching vibration due to the surface adsorbed moisture or hydroxyl group is observed in PJW sample but less pronounced in Biochar. The -CH₂- symmetric stretch peaks of an alkyl at 2992 cm-¹ was also observed on the FT-IR spectra of both PJW leafs and the prepared Biochar. Meanwhile, the C=O stretching vibration at 1725 cm-¹ and the C=C stretching variation aromatic ring were present in the both PJW leafs and the prepared Biochar.
It was noted that all the functional groups prominent in the PJW leafs were retained in Biochar after the carbonization. However, the FT-IR of the fingerprint region in both PJW leafs and the prepared Biochar was not similar. There is an obvious improvement in the acidic functional groups on the produced biochar surface in comparison with the PJW. This is an indication that the PJW leafs have been converted to entirely new product by its carbonization [28].
Surface Morphology of the Prepared Biochar
The produced Biochar from carbonization of PJW has a significantly oxygenated functional groups on its surface as presented by the Scan Electron Microscope (SEM) (Figure 3). There is a clear reduction in the surface porosity of the produced Biochar. The superiority of the surface oxidized Biochar in term its hydrophilicity was reported by Singh et al., (2016). The high hydrophilicity and wettability of the biochar surface will lead to an enhanced binding with metals.
Energy Band-Gap of Biochar Supported-TiO₂
The energy band gap of TiO₂ and Biochar Supported- TiO₂ photocatalyst were measured using the Tauc plots. It was observed that the energy band gap of the synthesised TiO₂ nanoparticle and that of the Biochar Supported- TiO₂ were 2.81 eV and 2.11 eV respectively. The significant reduction in the energy band gap of Biochar Supported-TiO₂ photocatalyst was as a result of Ti-O-C bonds. The carbon 2p interacts with oxygen 2p atomic orbitals in an inert reaction environment (nitrogen) to produce a sub-band levels between the valence band (VB) and conduction (CB) [30]. The observed increases in the edge of the valence band, consequently caused the reduction in energy band gap [18]. In the current investigation, application of PJW biochar as a support for TiO2 lead to a significant modification in the morphological structure and reduction in the energy band gap. The Biochar supported-TiO₂ photocatalyst showed greater promise as a solar active photocatalyst.
SEM-EDS of the Synthesized TiO2 Photocatalyst
The SEM-EDS of TiO₂ showed Oxygen (41.10 %) and Titanium (43.45 %) were presented in a near similar ratio, indicates the formation of Titanium oxide nanocomposite in its pure form (Table 3). Meanwhile, the SEM-EDS result for the Biochar Supported-TiO₂ showed the Oxygen (39.71 %), Titanium (24.29 %) and Carbon (34.49 %) as the main elements in the nanocomposite. The increased in % composition of carbon is a direct effect and indication of successful incorporation of Titanium within the Biochar. Likewise, an observed increased oxygen-titanium ration was due to formation of new oxygen bond. The resultant oxygen vacancy is responsible for lower energy gap and consequently reduction in electron recombination associated with the titanium oxide photocatalyst.
Brunauer Emmet Teller (BET) Surface Area Analysis
The N2 adsorption-desorption isotherms of the synthesized TiO2 and Biochar Supported-TiO2 was presented (Figure 4). The adsorption-desorption isotherms exhibits a characteristics of mesopores solids resulting with type IV adsorption isotherm undergoing capillary condensation and hysteresis during desorption [31].. Different parameters were obtained for the Brunauer-Emmett-Teller (BET) method surface area and Barrett-Joyner-Helanda (BJH) method poresize distribution. The BET surface area and adsorption average pore diameter of synthesized TiO2 were 11.11 m2/g, 9.793 Å respectively. And for the Biochar Supported-TiO2, the BET surface area and adsorption average pore diameter were 84.45 m2/g, 10.12 Å respectively.
The increased BET surface area and average pore diameter indicates that there is a reduction on the surface of titanium oxide as a result of the presence of biochar. The higher surface area and adsorption pore diameter in Biochar Supported-TiO2 ensure higher contact time, enhanced adsorption and photocatalytic efficiency [32].
X-ray Diffraction (XRD) Analysis
The x-ray diffraction patterns of TiO₂ and Biochar Supported-TiO₂ were provided in Figure 5. In this pattern, all lines can be indexed using the ICDD no. 00-001-1292. The position of 2θ corresponds to Miller indices of (110), (101), (111), (211), (220), (002), and (301) crystalline planes. The distinctive peaks at 2θ angles in the synthesized TiO₂ are corresponding to the rutile phase. Meanwhile, the distinct peaks in Biochar Supported-TiO₂ at (220), (301), and (200) crystalline planes showed the characteristic anatase phase. Therefore, there is a mixture of rutile and anatase crystalline phase in the Biochar Supported-TiO₂ due to the influence of Biochar. According to Zhang, (2017), photocatalysts with anatase and rutile phases are more efficient than those with only one crystalline phase.
Application of the Biochar Supported-TiO2 as a Photocatalyst in the Degradation of Orange II Sodium Azo-Dye
The ability of the Biochar Supported-TiO₂ to act as a photocatalyst at various reaction conditions was investigated through the photochemical degradation (Visible light) of an orange II sodium (OR2) Azo-dye in simulated textile wastewater. A quantity of OR2 equal to 100mL in a 250 mL glass container was subjected to degradation (100 rpm, 30 degree Celsius) by exposure to a 160 W Mega-Ray irradiation lamps light with UV filter (450 nm). The solution was initially set-up in the dark for 20 minutes to allow the adsorption-desorption equilibrium between the photocatalyst (TiO₂) and OR2 molecules. The reaction setup was subjected to the various condition as presented in Table 4. Thereafter, the samples were centrifuged and then analysed with the aid of UV-Visible Spectrophotometer to determine the % degradation.
The calibration curve for the absorption spectra of Orange II Sodium salt (OR2) for concentrations ranging from 2 ppm to 10 ppm was obtained by measuring the respective absorbance of the prepared OR2 concentration (λmax = 483 nm). This was done in other to be able to determine the concentrations of OR2 during the batch photodegradation experiments.
Effect of Photo-Catalyst Loading
An amount of the synthesized TiO₂ and Biochar Supported-TiO₂ between 50 mg/L and 200 mg/L were applied in a reaction chamber for the photodegradation reaction of OR2. The OR2 photo-degradation was very poor (12.47 %) when the synthesized TiO₂ was applied and there was no significant improvement in the OR2 photodegradation despite the increased in the TiO₂ photocatalyst dosage. Meanwhile, Biochar Supported-TiO₂ on application, gave a relatively higher % photodegradation (28.58 %) with increased degradation efficiency (55.34 %) as the amount of the Biochar Supported-TiO₂ increased (Figure 6).
The photo-degradation efficiency of OR2 during the application of Biochar Supported-TiO₂ was directly proportional to the catalyst loading. This indicated a true catalytic regime that can be attributed to the increased photo reactive sites on the surface of Biochar. The photo-reactive is capable of enhanced photocatalytic activity in the TiO₂ nanocomposite [33]. The noticed reduction of photo-degradation efficiencies maybe due to increased turbidity of OR2 solution and the consequential low light penetration [8].
Impact of Solution pH on Photodegradation of OR2
The photocatalytic efficiency of the Biochar Supported-TiO₂ was strongly affected by the OR2 solution pH. Highest photocatalytic efficiency of OR2 was recorded for the Biochar Supported-TiO₂ (83.48 %) at pH 6 while the lowest (73.08 %) was attained at pH 10 (Figure 7). The results showed that the influence of solution pH at an acidic and neutral pH conditions were more favourable than that of the basic conditions. This suggests that the photophysical generation of free radical oxidants such as hydroxyl radical was more intense in an acidic and neutral OR2 solution [34].
A higher photocatalytic efficiency was observed in a neutral medium due to the non-dissociative nature of the dye which lead to a strong adsorption onto the catalyst surface. The noticed decrease in photo-degradation efficiency was a resultant effect of the negatively charged nature of the photocatalyst surface and the resultant poor surface activity in a basic medium [35].
Effect of Initial Dye Concentration
A decreased photo-degradation efficiency was noticed as the concentration of ORS exceeded 20 ppm (Figure 8). This can be accounted for by the opacity nature of the concentrated OR2 which prevented the photo-degradation by blocking the light penetration. This implies that a well diluted textile wastewater is required for the photocatalytic treatment. Besides, the photo-degradation is more efficient in the tertiary stages of water treatment [36].
Kinetics of the Photodegradation of Orange II Sodium Dye
The kinetic studies for OR2 photo-degradation using both TiO₂ and Biochar supported- TiO₂ were as presented (Figure 9). The photo-degradation of OR2 by the photocatalyst followed pseudo-first-order and aligned with the Langmuir-Hinshelwood kinetic model.
The high values of coefficient of determination (r2;) obtained for TiO₂ and Biochar Supported-TiO₂ kinetic plots in the current investigations implies a good correlations values in the linear regression models. This showed that the photo-degradation processes of OR2 in the presence of the TiO₂ and Biochar Supported-TiO₂ were governed by Pseudo-First-Order Kinetic Model [35,37]. The K values for TiO₂ and Biochar Supported-TiO₂ were compared (Table 5). It became apparent that the prepared TiO₂ had a lower photocatalytic activity under visible light in comparison with Biochar Supported-TiO₂.
Electrical Energy Efficiency per Order (EEo) of the Photocatalytic Degradation of OR2
The lowest value of EEo of 136.49 kWh/m3; was obtained using Biochar Supported-TiO₂ at pH 6.8. The results confirm that photocatalytic degradation is affected by the solution pH. Besides, it can observed that the Biochar Supported-TiO₂ offered a better energy efficiency at all tested pH (136.49 KWh/m3; at pH 6.8) compared to the unsupported TiO₂ (1182.19 KWh/m3; at pH 6.8)
Conclusion
The reported limitations in the photophysical application of TiO₂ under the solar radiation are caused by its large energy bandgap (3.0 - 3.20 eV) and electron recombination. Overcoming these issues has been achieved by modification through the synthesis of Biochar Supported-TiO₂. The biochar which was produced from leafs of an invasive plant (Acacia Saligna) was subsequently applied as a support during the synthesis of TiO2 nanoparticle. A massive reduction in the energy band gap (1.96 eV) was achieved in the mixed anatase/ rutile Biochar Supported-TiO₂ photocatalyst. The characterization of TiO2 doped biochar using methods such as SEM-EDS, FTIR, XRD and BET have showed that the TiO₂ was successfully immobilized on the Biochar external surface. The synthesized Biochar Supported-TiO₂ nanoparticles exhibiting small hysteresis phenomenon which represent a typical type IV adsorption isotherm attributed to mesosoporous material with a low porosity.
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Figure 2.
FTIR Spectra of PJW leaf and Biochar.
Figure 3.
SEM images of PJW leafs (A) and the Produced Biochar (B).
Figure 4.
BET N2 adsorption-desorption isotherms of the synthesized TiO2 and Biochar Supported-TiO2.
Figure 4.
BET N2 adsorption-desorption isotherms of the synthesized TiO2 and Biochar Supported-TiO2.
Figure 5.
XRD pattern of TiO₂ and Biochar supported-TiO₂.
Figure 6.
Effect of Photocatalyst Loading on the Efficiency of Photodegradation of OR2 (OR2 concentration =20 ppm, pH = 6.8, Exposure time = 60 min).
Figure 6.
Effect of Photocatalyst Loading on the Efficiency of Photodegradation of OR2 (OR2 concentration =20 ppm, pH = 6.8, Exposure time = 60 min).
Figure 7.
The % Photodegradation of OR2 Solution at Varied pH.
Figure 8.
Effect of initial dye concentration on the photodegradation efficiency of OR2 [Ccat =200 mg/ L, pH = 6.8, time = 60 min].
Figure 8.
Effect of initial dye concentration on the photodegradation efficiency of OR2 [Ccat =200 mg/ L, pH = 6.8, time = 60 min].
Figure 9.
The Photo-degradation Kinetics of OR2 in TiO₂ and Biochar Supported-TiO₂ [Ccat= 200 mg/L, pH= 6.8].
Figure 9.
The Photo-degradation Kinetics of OR2 in TiO₂ and Biochar Supported-TiO₂ [Ccat= 200 mg/L, pH= 6.8].
Table 2.
Yield and chemical compositions of the Biochar from PJW Leaf [PJW leafs weight = 10.0 g; temperature = 250 oC].
Table 2.
Yield and chemical compositions of the Biochar from PJW Leaf [PJW leafs weight = 10.0 g; temperature = 250 oC].
| Pyrolysis | Yield (%) | Carbon (%) | Oxygen (%) | Others elements (%) |
|---|---|---|---|---|
| Time (hours) | ||||
| 1 | 68.90 | 78.62 | 19.05 | 2.33 |
| 2 | 70.90 | 75.11 | 22.26 | 2.63 |
| 3 | 70.58 | 77.57 | 19.30 | 3.14 |
Table 3.
SEM-EDS Showing Chemical composition of TiO₂ and Biochar Supported- TiO₂.
| Elements | TiO₂ (Wt %) | TiO₂-supported Biochar (Wt %) |
|---|---|---|
| Titanium | 43.45 | 24.29 |
| Oxygen | 41.40 | 39.71 |
| Carbon | 15.14 | 34.59 |
| K | 0.61 |
Table 4.
Reaction Design for the Application of Photocatalysts .
| OR2 Concentration (ppm) | Amount of Photo catalyst (mg/L) | Time (Minutes) | OR2 Solution pH |
|---|---|---|---|
| 20 | 50 | 60 | 6.8 |
| 30 | 50 | 60 | 6.8 |
| 40 | 50 | 60 | 6.8 |
| 50 | 50 | 60 | 6.8 |
| 20 | 50 | 60 | 6.8 |
| 20 | 100 | 60 | 6.8 |
| 20 | 150 | 60 | 6.8 |
| 20 | 200 | 60 | 6.8 |
| 20 | 50 | 5 | 6.8 |
| 20 | 50 | 10 | 6.8 |
| 20 | 50 | 15 | 6.8 |
| 20 | 50 | 20 | 6.8 |
| 20 | 50 | 60 | 4.0 |
| 20 | 50 | 60 | 6.0 |
| 20 | 50 | 60 | 8.0 |
| 20 | 50 | 60 | 10.0 |
Table 5.
Kinetic parameters of OR2 Photo-degradation in TiO₂ and Biochar Supported-TiO₂.
| Photocatalyst | OR2 concentration (ppm) |
K₁ x 10- 3 (Second-1) |
r2; |
1/K (Seconds) |
|---|---|---|---|---|
| 20 | 10.2 | 0.9041 | 98.3 | |
| TiO₂ | 30 | 7.5 | 0.9651 | 132.7 |
| 40 | 4.9 | 0.9823 | 202.2 | |
| 50 | 2.2 | 0.9776 | 442.8 | |
| 20 | 15 | 0.9914 | 66.7 | |
| Biochar Supported-TiO₂ | 30 | 13.2 | 0.9566 | 75.8 |
| 40 | 9.8 | 0.9700 | 102 | |
| 50 | 7.8 | 0.9504 | 128.2 |
Table 6.
Electrical Energy Efficiency per order (EEo) and Kinetic parameters of OR2 for the TiO₂ and Biochar Supported-TiO₂ at varied solution pH [OR2 concentration = 20 ppm, Photocatalyst concentration = 200 mg/ L, Time = 60 min, power= 160W].
Table 6.
Electrical Energy Efficiency per order (EEo) and Kinetic parameters of OR2 for the TiO₂ and Biochar Supported-TiO₂ at varied solution pH [OR2 concentration = 20 ppm, Photocatalyst concentration = 200 mg/ L, Time = 60 min, power= 160W].
| Photocatalyst | pH | Removal (%) |
Kx10-3 (min-1) |
r2; |
EEO (kWh/m3) |
|---|---|---|---|---|---|
| 4 | 20.75 | 1.94 | 0.7170 | 1056.75 | |
| TiO₂ | 6.8 | 18.77 | 1.73 | 0.7719 | 1182.19 |
| 8 | 16.32 | 1.49 | 0.8766 | 1379.36 | |
| 10 | 12.96 | 1.16 | 0.8273 | 1770.58 | |
| 4 | 81.73 | 14.17 | 0.9549 | 144.57 | |
| Biochar Supported-TiO₂ | 6.8 | 83.48 | 15.01 | 0.9525 | 136.49 |
| 8 | 77.81 | 12.53 | 0.9677 | 163,39 | |
| 10 | 70.03 | 10.94 | 0.9435 | 187.22 |
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