La-doped TiO2 Nanoparticles for Photocatalysis: Synthesis, Activity in Terms of Degradation of Methylene Blue Dye and Regeneration of Used Nanoparticles

In this study, bare and Lanthanum (La)-doped TiO2 photocatalysts Ti1−xLaxO2 (x = 0.00–0.025) were prepared by employing a solution-combustion procedure. In this, citric acid was utilized as fuel and as a complexing agent. The prepared photocatalysts were characterized by FTIR, FE-SEM, XRD, DRS and XPS. The XRD confirms that prepared TiO2 photocatalysts have only the anatase phase, and also, crystallite size was calculated which is 30.16 and 19.90 nm for bare and Ti0.985La0.015O2, respectively. The DRS shows that with increasing the doping concentration of La in TiO2, a continuous shifting in absorbance towards the visible light region was observed. The FTIR determines the O–H band, Ti–O–La, and several other functional groups present in the synthesized bare and La-doped TiO2 photocatalysts. The XPS spectra confirm the existence of all expected elements (Ti, O, and La) in the synthesized photocatalysts. The FE-SEM confirms spherical shape of prepared photocatalysts, and particle size of bare and Ti0.985La0.015O2 was 32.28 and 22.24 nm, respectively, which agrees with XRD data. Photocatalytic breakdown of methylene blue (MB) dye in its aqueous solutions of different concentrations (10, 20, 30, 40 and 50 ppm) was found to be first order. The best activity was shown by Ti0.985La0.015O2, and it was better than the commercial aeroxide P-25 photocatalyst. The Ti0.985La0.015O2 catalyst could be regenerated and reused up to five times with a minor loss in degradation efficiency of MB dye (30 ppm) about 7.85% at the end of fifth cycle, however, with fresh catalyst degradation was 88.71%.


Introduction
Various water contaminants, primarily dyes, occur due to recent industrial development and improvement in standard of living.The organic dyes are frequently used to produce textiles, leather and papers, generating loads of water pollution [1].Among various dyes used in these industries, methylene blue (MB) is an organic dye that is toxic; nonbiodegradable; environmentally persistent and stable to light, water, heat and oxidation.MB dye is a widely utilized basic and cationic dye with an array of applications.However, when discharged into water bodies, MB poses a significant threat to aquatic animals' life.Exposure to MB can cause detrimental effects such as a rapid heartbeat, nausea, New methods for wastewater treatment are constantly being established to completely degrade toxins without negatively impacting the atmosphere or human health.Advanced oxidation processes (AOPs) have been considered for usage in wastewater purification in recent decades, aiming to complete mineralization of pollutants into harmless end products [11].Various AOPs such as vacuum-UV (VUV) photolysis, photocatalytic oxidation, UV/O 3 , UV/H 2 O 2 and fenton-like processes are used [12].To eliminate various forms of organic and inorganic pollutants from aqueous solutions nonselectively, AOPs utilize hydroxyl free radicals (•OH) and reactive oxygen species, which, once produced, are highly effective and intensely oxidizing species.AOP is preferred over other methods because they are environment friendly as they neither transfer pollutants from one phase to another nor they produce hazardous sludge upon treatment of pollutants [13].
Solar photocatalysis using TiO 2 semiconductor is one of the AOP techniques used to produce •OH free radicals.The ability to use radiation from the sun to stimulate the photocatalyst is another advantage of this technology.In that situation, the cost of the treatment would be far lower than the cost of using artificial radiation, and it might be more readily applied in the industry [14,15].Because of its beneficial properties, non-toxicity, low cost, chemical stability, and environmental sensitivity, titanium dioxide (TiO 2 ) has been accepted as an inherent semiconductor material for the breakdown of hazardous organic compounds in aqueous solution [16].
The most popular photocatalyst for air purification and wastewater treatment is TiO 2 .However, because photogenerated pairs of electron and hole recombine quickly, the photocatalytic degradation efficiency is still relatively low.So, a current key obstacle in this field is enhancing photocatalytic efficiency.It has been demonstrated that doping in the lattice of TiO 2 is an efficient way to surge the activity of photocatalysis [17].Rare earth ion doping surges considerably the photocatalytic performance of TiO 2 , and by capturing photogenerated electrons, it can also improve the efficiency of electron-hole pair separation [18][19][20][21][22][23].
Pairs of electron and hole are generated when a semiconductor, such as TiO 2 , is subjected to light quanta with energies higher than that of the band gap.These photoexcited species (e + /h + ) can diffuse on the surface of photocatalyst and interact with molecules that have been adsorbed in redox processes.The principal reactions are the oxidation of water molecules or OH − by holes to create •OH free radicals because water molecules outweigh contaminant molecules.The superoxide radical ( .O 2 − ), a lesser reactive species of oxygen than the radical •OH, which can strike the organic substances or, through various events, ultimately release the •OH free radical, is also produced when a photogenerated electron reacts with adsorbed oxygen and this •OH free radical breaks organic substances [24,25].
Unfortunately, TiO 2 's industrial utilization is constrained by its broad band gap values and fast recombination rate of photogenerated pairs of hole and electron [26].Metal ions such as Cu, Fe, Mn, and Co [27][28][29] and non-metal ions such as S, N, C, F, I and B [30][31][32][33] doping are used to improve the characteristics of TiO 2 .Researchers' attention is now focused on rare earth elements, i.e.Er, La, Eu and Ydoped titanium dioxide.La-doped compounds are commonly utilized as competent catalysts resulting from 4f electron transition.
Rutile-anatase transition in TiO 2 doped with La is radius dependent.The large atomic radius has a more significant inhibitory effect on anatase-rutile TiO 2 transformation [34].
Recent publications have revealed that doping rare earth elements reduce band gap values of TiO 2 [34,35].This sparked the idea of doping TiO 2 with La to create an effective photocatalyst.In present work, La has been doped in TiO 2 to reduce the band gap so that visible light may be used for photocatalysis.Also, La doping promotes the separation of electrons and holes and reduces rate of recombination of the charge carrier and hence, La doping improves TiO 2 photo reactivity.
As far as we know, this paper covers the synthesis of TiO 2 doped with La using inexpensive TiO 2 powder by straightforward citric acid-assisted solution-combustion procedure and annealing to increase the crystallinity of the nanoparticles.The conditions under which the particles were produced significantly impacted their size and form.The activity of nanoparticles as photocatalyst was determined by kinetics photodegradation of MB dye.

Chemicals Used
The chemicals employed in the preparation of TiO 2 nanoparticles are as follows.TiO 2 powder with a purity of 99%, ammonia sulphate GR [(NH 4 ) 2 SO 4 ], sulfuric acid (H 2 SO 4 ) 98%, liquor ammonia sp.gr. is 0.91 (about 30% NH 3 ), lanthanum nitrate with a purity of 99%, citric acid monohydrate GR (C 6 H 8 O 7 H 2 O), MB dye and Nitric acid GR (HNO 3 ).All of the above chemicals were acquired from Merck, India.

Synthesis of Doped TiO 2 Nanoparticles
The doped TiO 2 crystalline nanoparticles were synthesized by solution-combustion process from TiO 2 powder in a similar manner as reported earlier [27,33,36,37].The process is described for 1 mol % La doping.The 4.7289 g of TiO 2 was dissolved in 100 mL of sulphuric acid, and six times mol of TiO 2 ammonium sulphate was added.The resulting solution was heated with the hot plate using a magnetic bead at about 400 rpm for 2-3 h at a temperature of 180 °C, which resulted in titaniumoxysulphate, TiO(SO 4 ).In another beaker, lanthanum nitrate (0.000626 mol) was added to 50 mL sulfuric acid for 1% La doping, and for other La doping, the La(NO 3 ) 3 amount was added according to stoichiometry.The hot plate was used to heat the resulting dispersions with the help of magnetic stirrer at about 300 rpm for 2-3 h at 170 °C.Then, both solutions were mixed hot and cooled to ambient and using distilled water made up to 500 mL of total volume.
Then, ammonia (NH 3 ) solution was added gradually so that a white residue was obtained, which was separated through the Buchner funnel.This residue was mixed with 100 mL of HNO 3 to form titanium oxynitrate, TiO(NO 3 ) 2 .About 10 g of complexing agent, i.e. monohydrate citric acid, was added, and the total solution was made up to 500 mL by adding double-distilled water.After that, the entire contents were evaporated over a hot plate at 70-80 °C with steady stirring till self-ignition occurred.Ignition took place in an open atmosphere at ambient temperature, and burning occurred by self-promulgating combustion, evacuating significant gases and forming a fluffy brown mass of La-doped TiO 2 that was crushed into powder with a pestle and mortar.Citric acid is utilized as a complexing agent, forming a complex with cations and acting as fuel for the combustion process in the ignition step.The temperature was uplifted by the ignition stage, which resulted in the formation of crystalline powder at a low temperature.The powdered La-doped TiO 2 product was calcined in the presence of the air for 5 h at 500 °C.This resulted in the final TiO 2 nanoparticles doped with La.

Characterisations
Employing XRD analysis with Cu-K irradiation (Rigaku Ultima IV, Japan), the average particle size and phase of the obtained undoped and La-doped TiO 2 (with 0.005, 0.01, 0.015, 0.02, and 0.025%) nanoparticles were examined.When determining the band gap energies of the synthesized photocatalysts, the Kubelka-Munk method was used to analyse the data from the DRS analysis (CORY 100 Bio UV spectrophotometer) using barium sulphate as the reference.The Nicolet 5700 (Thermo Electron) FTIR spectrophotometer was used to record the infrared spectra using the KBr pellet method.Using monochromated Mg-K (1253.6 eV) as the Xray source (AMICUS, Kratos Analytical, England), the XPS analysis was performed to determine the chemical state and binding energy of elements contained in the produced photocatalysts.XPSPEAK41 and ImageJ software were used to analyse XPS and FESEM data, respectively.All the graphs were plotted using Origin 2019b software.

Photocatalytic Reactor for the Degradation of Dye Solution
The synthesized Ti 1−x La x O 2 (x 0.00, 0.005, 0.01, 0.015, 0.02 and 0.025) nanoparticles were used to photodegrade the MB dye in UV photochemical reactor (UV-PCR).
The UV-PCR (Fig. 1) is fortified with 8W UV tubes (Philips TUV 8W G8T5 Hg) and a stirrer obtained from Perfit India Limited, Ambala, India.Dye solutions were treated in a quartz tube throughout.Only 100 mL of dye solution and nanoparticles was treated so that it properly mixed during the photolysis reaction.The 100 mL of the MB solution was taken without any photocatalyst and put in UV-PCR and exposed to UV light for 3 h to assess the self-degradation of dye.A 2 mL sample was tested for dye concentration every 10 min during the process.
The dye is also adsorbed on the surface of the photocatalyst.Adsorption studies were therefore performed to know the affinity of dyes for the photocatalysts.100 mL solution of the dye was placed in the tube, and 0.01 g of the photocatalyst was mixed to it to investigate and the dye adsorption by photocatalysts.The tube was covered with black foil to prevent photocatalysis by ambient visible light.The tube was maintained for 1 h with constant agitation in UV-PCR, and its lights were not made on. 2 mL of dye solution was drawn from the tube after every 10 min and centrifuged, and dye concentration was determined.
The experimental methods described above were used throughout.The photocatalyst Ti 0.985 La 0.015 O 2 exhibited the highest photocatalytic activity amid all prepared photocatalysts and was therefore used in this study to measure the activity of photocatalysis.
By deducting the decrease in dye concentration because of adsorption on photocatalyst and the deficit of dye due to autolysis in solution, the true decrease in dye in simulated solution of dye because of photodegradation by the photocatalyst was estimated.The photocatalytic degradation of MB dye in the simulated dye solution was calculated by the formula: [33] (1) Change of concentration by photo degradation

Reusability of Used Photocatalyst
The performance of used 1.5% La-doped TiO 2 photocatalyst for degradation of aqueous MB dye was explored after Fig. 1 Graphical representation of UV-photochemical reactor regeneration.The regeneration was done five times after each use.The photocatalyst was regenerated using the following method.To separate the photocatalyst loaded with dye from the overall solution, the entire mixture of photocatalyst and photodegraded dye was centrifuged at 3000 rpm for 20 min and the photocatalyst was deposited at the bottom and separated.With this double-distilled water was added and again centrifuged for 20 min at 3000 rpm and a photocatalyst loaded with dye was separated at bottom.This photocatalyst slurry was put into a glass petri dish, and its water was evaporated in a drier at 102 °C.The dye-loaded, La-doped nanoparticles were taken out and put in the crucible to undergo a five-hour calcination process at 500 °C to get a regenerated catalyst, ready for use.

Methodology of Kinetic Study
100 mL of the dye solution was introduced into quartz tube of the UV-PCR for dye degradation kinetics analysis, and 0.01 g of prepared nanoparticles was added to this tube.After inserting magnetic bead, the tube was put inside the UV-PCR to allow the dye to be photodegraded.The dye starts to photodegrade as soon as the UV PCR lamp was switched on.Constant stirring was used to comprehensively mix the dye solution and photocatalyst during the photocatalytic process.A 2 mL sample was collected from the tube after every 5 min and centrifuged for 2 min before measuring its concentration.The same procedure was used with all catalysts.The different catalysts prepared with La doping (0, 0.5, 1, 1.5, 2.0 and 2.5%) were used, and dye concentrations in solution were 10, 20, 30, 40 and 50 ppm.For comparison of catalysts, the

XRD
X-ray diffraction was used to understand the consequence of various percentages of La doping in TiO 2 and investigate the crystal structure.In Fig. 2, XRD plots for undoped TiO 2 and doped TiO 2 have been shown.All the prepared nanoparticles have anatase phase without any significant rutile phase [38].
Figure 2 also shows that doping of La within TiO 2 does not same as bare TiO 2 .The peak at the 2θ (25.351) corresponds to plane alter the structure of TiO 2 as it remains 101 of anatase phase.Meanwhile, Lanthanum ionic radius has the value of 1.03 Å which is greater than that of Titanium, which has a value of 0.62 Å, so it cannot replace the Ti ion and leftovers at interstitials of Titanium dioxide beneath the range of scan of XRD.So, these dissimilarities between La and Ti ions radii may create bonds of Ti-O-La or lanthanum oxide (La 2 O 3 ) at the anatase surface relative to actual assimilation of La 3+ in the lattice of the TiO 2 .The La 2 O 3 peak is not present in the XRD plot because it is scattered and cannot be discovered in the XRD pattern [35].It is also evident from Fig. 2 that on increasing doping percentage of La, the intensities of prepared samples also increase significantly.With a rising La percentage of doped nanoparticles, notably for anatase phase, values of crystallite size of synthesized Ladoped TiO 2 samples significantly diminish and recombine capacity of pairs of electron-hole on excitation of La 3+ on TiO 2 is inhibited, promoting the activity of photocatalysis of prepared photocatalysts [39].
where d is crystallite size, β is full width at half maximum, λ is radiation wavelength (1.5406 Å), and θ is the angle of diffraction.
The average crystallite size of TiO 2 and 1.5% La-doped TiO 2 was found to be 30.16and 19.90 nm, respectively.A similar result would also be found by Zhan et al. [41].

FTIR
Fourier transform infrared spectroscopy was applied to detect distinct functional groups in the lanthanum-doped and undoped TiO 2 photocatalysts.The FTIR spectra presented in Fig. 3 show the stretching vibrations of OH functional group at the wavenumber of 3450 cm −1 .All the La-doped and undoped photocatalysts peak at the wavenumber of 1020 cm −1 , which relates to the anatase phase of Ti-O vibrations.Undoped TiO 2 shows a band at the wavenumber of 512 cm −1 , a characteristic peak of TiO 2, but with doped TiO 2 with La, this characteristic peak shifts at 480 cm −1 , which might correspond to bond structure of Ti-O-La.Sibu et al. [42] also reported these results in a similar range.The band spectra situated at the wavenumber of 1620 cm −1 validate the occurrence of OH groups at photocatalysts' surface, also called bending vibrations of the water (H-O-H bending) molecules which are absorbed at the surface of nanoparticles.Nie et al. [43] and Coromelci et al. [44] also reported

DRS
The optical absorbance spectra of synthesized TiO 2 doped with La and bare TiO 2 were measured in the UV-visible range and are presented in Fig. 4. The indirect band gap of bare TiO 2 and doped with La was calculated with the help of the plots of [F(Rα)*hυ] 1/2 versus hυ (Fig. 4), where F(Rα) is called the Kubelka-Munk function and may be represented as: (3) where Rα 10 −A is the reflectance coefficient of catalyst determined from absorbance data.It is noticeable from inset of Fig. 4 that band gap values of prepared nanoparticles are decreased from 3.2 to 2.7 eV on rising doping percentages of lanthanum from 0 to 2.5%.Nie et al. [43] also reported a decrease in band gap values on increasing La doping in TiO 2 photocatalysts.
Results show that metals addition into TiO 2 photocatalysts causes a slight reduction in band gap values.This variation in band gap values may be the result of the dielectric confinement effect.The occurrence of this type of band corresponds to the displacement of charge to conduction band from valence band of TiO 2 (because of 2p orbital of oxygen).Due to the fact that the dielectric constant of La 2 O 3 is lower than that of TiO 2 , the energy change brought on by dielectric confinement (due to doping of La) is more significant than that brought on by the impact of space limitations on electron holes and which is evident from the decrease in band gap values is therefore detected that is known as red-shift [45].

FE-SEM
FE-SEM was used to conduct the morphological and microstructural analysis of the prepared bare and La-doped photocatalysts.In Fig. 5, FE-SEM images of the prepared photocatalysts bare and 1.5% La-doped TiO 2 are shown.From these pictures, it is evident that photocatalysts are of spherical shape.It is also clear from these figures that the morphology of doped photocatalysts remains unchanged, and some agglomeration may be due to the magneto-dipole interaction.It is also accomplished that doped photocatalysts' particle size is decreased compared to undoped one, having sizes approximately 22.24 and 32.28 nm, respectively.It agrees with the XRD data.This is beneficial because when size of the particle is decreased, surface area is increased, which enhances photocatalytic sites, which eventually increases photocatalytic activity of prepared samples [45][46][47].

XPS
The XPS was applied to analyse the composition of elements present at the surface and the chemical oxidation state of nanoparticles [48].Figure 6a represents the full scan spectra which confirms the presence of O and Ti elements on the bare TiO 2 's surface and presence of O, Ti and La on 1.5%-doped TiO 2 's surface.
In Fig. 6b, XPS spectra of 2p orbital of Ti are represented in bare TiO 2 and 1.5% La-doped TiO 2 .Both doped and undoped samples show two noticeable peaks attributed to Ti 2p 3/2 and Ti 2p 1/2 , respectively, indicating that the normal tetravalent oxidation state of titanium predominates Ti 4+ in anatase TiO 2 [49].The binding energy of undoped TiO 2 sample is 458.6 and 464.4 eV.After doping of La 1.5% binding energy increases by 0.2 eV and peaks shifts to higher values which shows the existence of various electronic interactions amid Ti and oxides of La because of their difference in electronegativity, which lowers Titanium external electron density and therefore, raises Ti 2p's binding energy [50].
In Fig. 6c, XPS plot of undoped TiO 2 for O 1s is shown.The peaks at binding energy of 529.3 eV and 531.1 eV are accredited to lattice oxygen and OH group, respectively, in undoped TiO 2 samples.In Fig. 6d, XPS plot for 1.5% Ladoped TiO 2 has been shown for O 1s in which two peaks are observed at the binding energy of 529.5 eV and 531.3 eV, which are more than that of 0.2 eV and a third peak is shown at the binding energy of 532.3 eV, which corresponds to the La-O bond and is further confirmed by FTIR analysis.Figure 6e depicted the La 3d spectrum of 1.5% La-doped TiO 2 .In this figure, the peaks endorsed to the spin split orbit La 3d 3/2 and La 3d 5/2 levels, indicating that the presence of La 3+ species is represented at 853.2 and 836.5 eV, respectively [51,52].In the literature, binding energies values of 3d shift of La are given as 851.8 eV and 834.9 eV, but here, it is found that these values shift to greater energy levels.This is possible because of the replacement of Ti 4+ by La 3+ , so it is clear that there is no incorporation of La in TiO 2 's lattice rather than in the configuration of Ti-O-La bond [53][54][55].The reason for shifting binding energies in doped TiO 2 is that La is less electronegative than Ti, so charge disparity occurs.As a result, the binding energy alters, and the La electron density in the Ti-O-La decreases [56].
As described earlier in Fig. 6d, the presence of La-O bond can confirm the dopant La has entered the lattices.The oxygen vacancies for charge compensation can be caused by the progress of the acceptor La 3+ ions into TiO 2 [57] as following:

Mechanism
Photocatalytic activity of undoped and La-doped TiO 2 nanoparticles was determined by measuring the variation of concentration due to degradation of MB dye solution during photocatalysis in UV-PCR.First, it is well acknowledged that doping with La is likely to develop an oxygen vacancy.The oxygen vacancy may then operate like a trapper to prevent pairs of electrons and holes from recombining, which are photo-generated [58].Additionally, Wu et al. [59] revealed that when La is doped in TiO 2 , it can convert Ti 4+ to Ti 3+ via charge compensation.La doping may cause impurity levels due to coaction of Ti 3+ and oxygen vacancies, which might prevent charge carriers from combining.The other benefit of photocatalytic activity is that La 2 O 3 on surface of TiO 2 might move electrons onto the surface.The space charge area gets smaller, and the surface barrier increases as the dopant percentage (La) increases.Additionally, the depth of light penetration into titania significantly surpasses space charge film when the dopant percentage is too prominent.Space charge area becomes quite constrained; as a result, it is simpler to recombine the photogenerated electron-hole pairs [53].When a photon of appropriate energy is incident on photocatalyst, the electrons are ejected, leaving behind holes.The electrons combine with oxygen to form superoxide.This superoxide radical and holes combine with H 2 O to give OH .Radicals [60,61].The radicals O 2 −. and OH .are highly reactive and oxidise and degrade the organic dyes in the simpler inorganic products [62,63].The different equations have These equations are given below as follows:

Kinetics Study La-Doped TiO 2
All the catalysts' kinetic analyses were completed, and Figs.7 and 8 depict kinetic data for degradation of MB dye in its The current results are comparable to various previous literature given in Table 2 aqueous solution with 1.5% La-doped TiO 2 photocatalyst.These figures show the concentration versus time data and the − ln(C/Co) versus time data, respectively.Pseudo-firstorder kinetics Eq. ( 8) was satisfactorily fitted to kinetic data of degradation of MB dye with all the catalysts as evidenced high R 2 values.
From the graph of − ln (C/Co) versus time, the k p values were determined and shown in Table 1 along with R 2 values.Compared to undoped TiO 2 , the catalysts' reaction rate has increased significantly by doping with lanthanum.TiO 2 doped with 1.5% La has the maximum reaction rate constant, which is consistent with other results [51].
It is impressive that the rate of MB's photocatalytic degradation first rises with an increased doping percentage of La before showing a reversal pattern after the amount of La reaches its optimum level.The space charger zone became small, which helped photogenerated pairs of electrons and holes separate effectively.As the percentage of La surged, specialized surface area expanded, and obstructions to the surface improved.The space charge area becomes extremely small when the percentage of La is very high, which might enable light to penetrate titania much deeper than the space charge layer.As a result, it is simpler to recombine for photogenerated charge carriers, and the photocatalytic activity would be decreased [55].
According to an adsorption investigation of the dye on the nanoparticles, only 1-2% of the dye was retained on the photocatalyst's surface.A negligible amount of the dye was photodegraded when no photocatalysts were present in the UV light source.
The reusability of photocatalysts is vital for industrial applications and economy.Figure 9 shows the results of the successive reusability experiments with best photocatalyst (1.5% La-doped TiO 2 ) performed for five cycles.Figure 9 reveals that degradation in 40 min continuously decreases (85.72-77.87%)from first to fifth cycle, however, with fresh catalyst degradation was 88.71%.So, there is a very small reduction in degradation efficiency (7.85%) after fifth cycle.It is also evident from Fig. 9 that the shape of all the curves is almost similar.The above analysis concludes that 1.5% Ladoped TiO 2 is highly stable throughout the photocatalytic degradation of MB dye.
Figure 10 displays the pictographic representation of photocatalytic breakdown of the MB dye of 30 ppm with 0.01 g of photocatalyst Ti 0.985 La 0.015 O 2 in UV-PCR at the time interval of 5 min.Here, in this sample 1, 2, 3,…, 10 represents MB concentration after time at 0, 5, 10,…, 45 min, respectively.
Aeroxide P-25 and the best-doped TiO 2 sample, Ti 0.985 La 0.015 O 2 , as well as the prepared undoped TiO 2 were compared; the results are given in Fig. 11.The results show that the TiO 2 doped with 1.5% La (Ti 0.985 La 0.015 O 2 ) displayed the best photocatalytic performance.
The doping of La could reduce the band gap hence providing a potential to use more part of solar spectrum for degradation of pollutants, and also, it can be used in solar cells for future research.

Conclusion
TiO 2 and La-doped [LaTi 1-x La x O 2 (x 0.00-0.025)]nanoparticles could be prepared by solution-combustion process.The prepared nanoparticles were characterized by XRD, FTIR, FE-SEM, DRS and XPS.Photocatalytic performance of each prepared bare and doped TiO 2 photocatalyst was assessed using UV-PCR.The kinetic investigations of all catalysts show that 1.5% La-doped TiO 2 nanoparticles have the best activity for the photocatalysis process in the UV-PCR reactor midst all the synthesized photocatalysts.The current study also discovered that as soon as the La concentration rises to 1.5%, so does activity of TiO 2 to photodegradation; however, the photocatalytic activity begins to diminish after doping concentration increases beyond 1.5%.At 1.5% La doping, TiO 2 had the maximum photocatalytic activity.The

Increase of time
where C a and C b are initial and ultimate concentrations in the dye solution, respectively.C c and C d represent the reduction in concentration due to dye adsorption and dye reduction in the final solution.

Fig. 6
Fig. 6 XPS spectra of a total spectra for TiO 2 and La-doped TiO 2 b fitting curves of the Ti 2p regions c fitting curve of O 1s region of undoped TiO 2 d fitting curve of O 1s region of 1.5% La-doped TiO 2 e fitting curves of La 3d regions

Fig. 7 Fig. 8
Fig. 7 Effect of residence time on removal of different concentrations of MB by Ti 0.985 La 0.015 O 2 photocatalyst

FeFig. 9
Fig.9 The reusability of 1.5% La-doped TiO 2 for the breakdown of MB dye at 30 ppm

Fig. 10 Fig. 11
Fig. 10 Pictographic depiction of degradation of MB dye of initial concentration 30 ppm in aqueous solution in UV-PCR reactor using 0.01 g Ti 0.985 La 0.015 O 2 photocatalyst

Table 1
Summary of the degree of fitting (R 2 ) and reaction rate constants of the undoped and La-doped TiO 2 photocatalysts

Table 2
Comparison of photocatalytic activity of various photocatalysts with different pollutants