Capability of TiO2 and Fe3O4 nanoparticles loaded onto Algae (Scendesmus sp.) as a novel bio-magnetic photocatalyst to degration of Red195 dye in the sonophotocatalytic treatment process under ultrasonic/UVA irradiation

In this study, the magnetic photocatalyst Scendesmus/Fe3O4/TiO2 was synthesized, and its sonophotocatalytic properties in relation to the degradation of the Red195 dye were evaluated. Particles were characterized using a scanning electron microscope (SEM), Fourier's transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and a vibrating-sample magnetometer (VSM). At a pH of 5, a photocatalyst dosage of 100 mg, an initial R195 concentration of 100 mg/l, an ultrasound power of 38W, and an exposure time of 20 min, the maximum Red195 removal efficiency (100%) was achieved. After five cycles of recycling, the composite's sonophotocatalytic degradation stability for R195 remains above 95%. Experiments on scavenging indicate that electrons (h+) and hydroxyls (OH-) are indispensable decomposition agents. The removal of R195 by Scendesmus/Fe3O4/TiO2 is consistent with the pseudo-first-order kinetic, Freundlich, and Henderson's isotherm models, as determined by kinetic and isotherm investigations. The negative activation enthalpy of the standard (ΔH°) illuminates the exothermic adsorption mechanism. The increase in standard Gibbs activation free energy (ΔG°) with increasing temperature reveals the process is not spontaneous. As indicated by the negative value of the standard entropy of activation (ΔS°), activation of the reactants resulted in a loss of freedom.


Prepration of algae (Scendesmus sp.)
The Caspian Sea Ecology Research Institute in Mazandaran, Iran, cultivated a sample of Scendesmus sp Algae.The samples were then transferred to the Gorgan University of Agriculture and Natural Resources laboratory.Using a super grinder, the microalgae were then ground as finely as possible 21 .

Synthesis of Fe 3 O 4 nanoparticles
For the synthesizing of Fe 3 O 4 nanoparticles, the sol-gel method was modified.To produce a golden solution, 65 ml of ethylene glycol and 4.95 g of ferric nitrate nonahydrate were stirred for two hours at 45 °C.After 10 h of increasing the temperature of the mixture to 95 °C, gel formation was obtained 22 .The emulsion was then centrifuged and desiccated in a 105 °C furnace for twenty hours (Memmert VO 400).The material was annealed for two hours at 450 °C in a vacuum furnace (Nabertherm, R80-750/11, Germany) to produce magnetic Fe 3 O 4 nanoparticles 6 .synthesis of Fe 3 O 4 /scendesmus 0.49 g of Fe 3 O 4 nanoparticles and 3.93 g of Scendesmus were dissolved in 60 ml of ethanol.At 73 °C, one hour was spent agitating the mixture.A solution of 6 ml ethanol and 1.58 ml diethanolamine was added dropwise to the initial mixture, which was stirred with a magnetic stirrer for 10 h at 76 °C until a dark brown solution was obtained.The solid was then isolated with an external magnet and dried in a vacuum furnace (Memmert VO 400) for 24 h at 90 °C23,24 .

Synthesis of scendesmus/Fe 3 O 4 /TiO 2
For one hour, a mixture of synthesized Scendesmus/Fe 3 O 4 and ethanol at a concentration of 99.9% was agitated.During 10 h of heating at 150 °C, the mixture was treated with 6.16 ml of tetrabutylammonium hydroxide (TBOT) and 60 ml of ethanol.After washing the sample with methanol and distilled water, it was calcined at 450 °C for three hours 6,22 . www.nature.com/scientificreports/

Point of zero charge
The point of zero charge (PZC) of algal biosorbent was determined with minor modifications to the salt addition method.The collection of various containers containing 0.1 M NaNO 3 concentrations.HCl and NaOH (0.1 M) solutions were used to obtain pH values ranging from 2 to 10 25 .Each vial obtained 1 g of algal biosorbent and was stirred at 160 rpm for 24 h.The pH of each filtrate was noted after its constituents.Calculating the PZC value of algal biosorbent by plotting the initial pH against pH change graph 26 .

Sonophotocatalytic experiments
Sonophotocatalysis was utilized in a US bath containing a UVA lamp to ascertain the R195 degradation rate.A precise amount of our prepared catalyst (0.25-1 mg/l) was added to a 250 mL Erlenmeyer Pyrex containing R195 at a determined pH (between 3 and 7).Using a pH meter, NaOH, and H 2 SO 4 , the initial pH adjustment was performed 27 .To better comprehend the effect of the parameters, the reactor was exposed to US frequencies (20-50 kHz) at UV light intensities (6 W).The concentration of 1 ml samples collected at different times (10-40 min) was determined using UV-vis spectrophotometry at 550 nm.Utilizing Eqs.(1) and ( 2), the degradation efficiency and reaction kinetics of R195 were determined: 28 q e in Eq. (1) quantifies the adsorbed ions (sorbate) in milligrams per gram in the biosorbent, where the initial and final metal concentrations C i and C e were measured by atomic absorption spectrometry; V represents the volume of the synthetic medium, and M represents the biomass of the biosorbent (g) 27,28 .

Desorption and regeneration studies
Using the supplied methodology, the reusability of the adsorbent to desorb the dye ions and regenerate the biomass for reuse was evaluated.To conduct an effective adsorption and desorption experiment, the aforementioned substances were subjected to five cycles of cycle repetition.0.1 M hydrochloric acid was used to desorb metal ions 29 .Desorption experiments were carried out by combining a metal-loaded adsorbent with 50 mL of desorption medium (0.1 M HCl) and agitating at 160 rpm 30 .Each cycle is dominated by sorption, followed by desorption and regeneration.The following equations characterize biosorbent desorption and regeneration performance 29,30 :

Isotherm modeling
Isotherm models help describe the interactions between contaminants and synthetic adsorbents.Langmuir, Freundlich, Temkin, and Harkins-Jura are the adsorption isotherms most frequently used.The Langmuir isotherm model depicts monolayer adsorption on a surface with restricted sites and no intermolecular interaction 8 .For a linear fit of the Langmuir isotherm model to the experimental data, the following equation was used: C e / q e versus C e (Eq.5).
where q e is the equilibrium adsorbate concentration in the adsorbent phase (mg/g), C e is the equilibrium adsorbate concentration in the aqueous phase (mg/l), and b is the constant associated with the free adsorption energy and the concentration at which the adsorbent reaches half saturation.q m also represents the maximum absorption capacity (mg/g) 5 .
The quantity of reversible adsorption on a heterogeneous surface increases with increasing concentration (Eq.6) according to the Freundlich adsorption isotherm 31 : where q m is the amount of molecules adsorbed to the adsorbent surface at any given time (mg/g), C e is the equilibrium concentration (mg/l), n and K F are the Freundlich constant and Freundlich exponent (mg/g (l/g)1/n, respectively), and C e is the equilibrium concentration (mg/l) 5 .
As demonstrated by the following equations (Eqs.7 and 8), the Temkin isotherm model is dependent on interactions between the absorbent and the adsorbate and assumes the linearity of the heat of adsorption of all molecules in the layer 32 : (1) Ci − Ce M (3) Desorption efficiency % = Amount of dye ion desorbed /Amount of dye ion adsorbed) × 100 (4) Photocatalyst efficiency = Regenerated removal capacity/Original removal capacity × 100 www.nature.com/scientificreports/b T is the Temkin isotherm constant (J/mol), R is the universal gas constant (8.314J/ mol K), T is the temperature (K), and A T is the Temkin isotherm equilibrium binding constant (l/g) 32 .
The fourth model examined to support the multilayer adsorption of iodine atoms onto the synthesized photocatalyst is the Harkins-Jura model, whose linear form (Eq. 9) is as follows 33 : where A H and B H are Harkins constants derived from the slope and intercept of the linear plots of q e 2 versus log C e , respectively 33 .

Kinetics modeling
Adsorption kinetics provides data on adsorbent performance and mass transfer modes, such as diffusion, surface adsorption, intramolecular adsorption, and chemical adsorption.Adsorption kinetics are typically consistent with the pseudo-first-order kinetic model when the adsorption control factor is located in the boundary layer 5 .It indicates that a change in adsorption rate is proportional to the accessible sites on the surface of the adsorbent.As demonstrated by Eq. ( 10) 8 : where q e1 and q t represent the quantity of adsorbate adsorbed at equilibrium time and time t, respectively (mg/g).K 1 (1/min) is the pseudo-first-order rate constant 5 .
In addition, the pseudo-second-order kinetic model is described as follows (Eq.11) 34 : where t is the time (min) and k 2 is the constant pseudo-second-order rate (g/mg min) 34 .
The Elovich model is one of the most commonly employed kinetic models for analyzing the impact of temperature on adsorption systems.The expression for the Elovich model is (Eq.12) 8 : where represents the initial adsorption rate constant (mg/g min) and Elovich's constant is the activation energy and surface coverage associated with chemisorption (g/ m 2 ) 8 .
According to the intraparticle diffusion model, the adsorption procedure consists of intraparticle diffusion, film diffusion, and emptying of the infill.This is crucial to the advancement of physical adsorption processes (Eq.13), as it accounts for the formation of multiple layers based on van der Waals forces 35,36 : where k int represents the intra-particle diffusion rate constant (g/mg min) and the intercept of the plot and C represents the boundary layer effect or surface adsorption 35,36 .

Thermodinamics modeling
The Arrhenius equation determines the activation energy, Ea, which is the minimum amount of energy necessary to initiate a chemical reaction 5 .
where kapp represents the apparent rate constant (min -1 ), Ea is the activation energy (kJ mol -1 ), T is the temperature (K), R is the gas constant (8.314J K -1 mol -1 ) and A is the Arrhenius constant (min -1 ) 22 .In the transition state theory (TST), the conventional Gibbs free energy, ΔG° (kJ mol -1 ), is defined by the following equations 6 : where ΔH° is the standard enthalpy (kJ mol -1 ) and ΔS° is the standard entropy (JK -1 mol -1 ) 5 .TST implies the temperature dependence of the apparent rate constant in the Henry equation 33 : www.nature.com/scientificreports/where K B is the Boltzmann's constant (K B = 1.380510 -23 JK -1 ) and h is the Planck's constant (h = 1.380510 -23 Js) 33 .
The ΔH ° and frequency factor constant (A) are analogous to the activation energy quantity (E a ) 6 .

Experimental design
Four independent variables were selected, including pH (A), photocatalyst dosage (B), exposure time (C), dye concentration (D), and US power (E) at three levels (Table 1).48 experimental trials were prescribed by the CCD-RSM, and the response of independent variables was fitted to the model using the following regression equation (Table 2): 5 .
where β 0 , b i , b ii , and b ij are the intercept, linear, squared, and interaction coefficients, respectively.Y denotes the response.In addition, x i 2 , x j 2 … x k 2 are the square effects, and x i x j , x i x k, and x j x k are the interaction effects of variables.k is the number of considered factors, and ε is the random errore 5 .

FTIR analysis
As determined by FTIR spectroscopy, Fig. 1 depicts the functional groups of Scendesmus/Fe 3 O 4 and Scendesmus/ Fe 3 O 4 /TiO 2 .Strong -OH stretching is detected at 3440.55 cm -1 in Scendesmus/Fe 3 O 4 /TiO 2 and scendesmus/ Fe3O4, which may be related to the presence of water 6 .The bands at 1164.35 and 1367.35cm -1 correspond, respectively, to the C=O, C-O, and Fe (C-O-Fe) stretching vibrations 22 .C=O at 1631.55 cm -1 , however, indicated the presence of acetylacetonate on the photocatalyst surface 5 .The Fe-O content of Scendesmus/Fe 3 O 4 and Scendesmus/Fe 3 O 4 /TiO 2 is also confirmed by bands between 511.06 and 590.14 cm -137 .The observed bands between 550 and 900 cm -1 verify the presence of Ti-O-Ti and Fe-O 6 .In addition to Fe-O stretching vibrations, symmetric and asymmetric stretching, and COO -, the bands are also associated with Fe-O stretching vibrations.Anatase Fe-O and TiO 2 are responsible for the peaks at 576 and 593 cm -1 in the Scendemus/Fe 3 O 4 /TiO 2 spectrum 37 .

SEM,Mapping and VSM analysis
Figure 2a and b depict the surface morphology of Scendesmus/Fe 3 O 4 /TiO 2 , respectively.Figure 2a demonstrates the octagonal shape and flat surface of the Scendesmus.sp 37.Scendesmus was uniformly coated with TiO 2 particles for photocatalytic activity, as shown in Fig. 2b 38 .This indicates that the titanium particles on the Scendesmus' surface are securely adhered.Therefore, the Scendesmus/Fe 3 O 4 /TiO 2 synthesis was successful.Carbon, iron, oxygen, and titanium are present in the mapping analysis, confirming the formation of Scendesmus/Fe 3 O 4 /TiO 2 (Fig. 2c-f) 39 .Based on VSM analysis, the presence of diamagnetic TiO 2 in the structure of Scendesmus/Fe 3 O/TiO 2 was responsible for a minor decrease in magnetic strength 5 .The photocatalyst exhibited robust magnetic activity (18) Table 1.Range levels of independent variables.www.nature.com/scientificreports/against a 1.4 Tesla external magnet.In addition, the saturation magnetization (MS) value was approximately 16 emu/g, demonstrating the photocatalyst's high magnetic properties (Fig. 3) 22 .

Model and statistical analysis
To design and optimize the interaction effects of five sono-photocatalytic process variables, the CCD model (RSM) was used.Table 2 displays the obtained results (actual and predicted responses) for the R195 degradation by means of the sono-photocatalytic process, after designating the number of trials using the CCD plan.Taking into consideration the coded factors, the proposed model equation (Eq.24) was fitted to the quadratic model for R195 degradation following statistical analysis.Table 3 presents a summary of the F-value, P-value, and R2 values used in the analysis of variance (ANOVA) to determine the significance and degree of fit of the employed model.The F-value and P-value for the degradation (24)   Red195 Removal(%) = + 90.57− 5.33 A + 1.06 B + 3.22 C + 2.39D + 0.06 AB − 0.1875AC − 1.19AD www.nature.com/scientificreports/ of R195 in the constructed model are 29.33 and 0.00001, respectively, indicating that the proposed model is significant 5 .As the factor with the highest F-value, the C-factor (dye concentration) is deemed significant.In addition, the P-value for lack of fit (LOF) reveals an insignificant mode (P-value > 0.05), which indicates a superior action compared to the model described 40 .Three categories of correlation coefficients, including R 2 (0.9560), adjusted R 2 (0.9234), and predicted R 2 (0.8566), were used to evaluate the suitability of the models (Table 4).Figure 4a was constructed from a comparison of predicted values against factual values 41 .The validity of the model was confirmed by a straight trend line connecting residuals (Fig. 4b).Comparing the residual's plot to the predicted values (Fig. 4c) and run numbers (Fig. 4d) requires a random dispersion.A Box-Cox procedure (Fig. 4e) was used to determine the normality of the data and establish the model significance of the sonophotocatalytic process 42 .

The effect of single factors
The variance analysis (ANOVA) for R195 removal is presented in Table 3.Among pH, exposure time, photocatalyst dosage, R195 concentration, and US power as a single variable, each factor with a high mean square and high F-value exerts the greatest influence on the sono-photodegradation of R195.Thus, the effect of variables on R195's degradation is 43 : The concentration of R195 with a mean square and F-value of 230.08 and 29.33, respectively, was the most crucial factor in R195 removal 5 .

Three dimensional response surface schemes
Three-dimensional (3D) graphical schemes (Fig. 5) were implemented in order to assess the individual and combined effects of operational variables on the sonophotocatalytic degradation of R195. Figure 5a depicts the simultaneous effect of initial pH (three to seven) and dye concentration (fifty to two hundred mg/lit) on optimization under constant conditions (exposure time = 22 min, US power = 65W, and photocatalyst dosage = 62.50 mg).Maximum removal efficacy was observed in a medium with a pH of 5 after 15 min.This trend can be attributed to the following elements: (a) A test apparatus operating under identical conditions will produce analogous results (equal production of hydroxyl radicals at each initial R195 concentration) 44 ; (b) the generation of hydroxyl radicals is proportional to the initial concentration of R195 40 .Therefore, an increase in the number of dye molecules can lead to the saturation of active sites on the surface of the photocatalyst and inadequate production of hydroxyl radicals 42 .(c) Produced intermediates of R195 during sonophotocatalytic degradation (at high concentrations of R195) reduce removal efficiency due to a competition reaction between the dye and intermediate with free radicals 5 .Dye molecules and photocatalyst nanorods are brought into favorable contact by increasing the number of accessible active sites.According to the scientific literature, the pka of R195 (3.6) and the pHpzc of TiO 2 (6.8) remind us that electrostatic interaction between the negatively charged facet of R195 (at pH > 3.6) and the positively charged facet of nanorods (at pH 6.8) is the primary reason for the accelerated degradation of R195 6,22 .Additionally, by undertaking sonophotocatalytic reactions in an acidic medium and extending the duration of US irradiation, residual R195 in the cavitation bubbles containing more hydroxyl radicals can provide a greater potential for oxidation of the model pollutant 44 .Amri et al. 45 and Nangia et al. 46 also reported similar results with our findings 45,46 .5b depicts the reciprocal effect of pH and photocatalyst concentration.By increasing the pH (from 3 to 7) and decreasing the amount of catalyst (from 100 to 25 mg), the removal efficiency was diminished.At a higher photocatalyst dosage, more cavitation bubbles may be produced in the region of ultrasound irradiation, resulting in sufficient free radical generation 22 .
Figure 5c investigates the effects of pH and US power on the elimination of R195 by varying the US power from 30 to 100 W and the pH from 3 to 7. As the US power increased from 30 to 100 W, the percentage of removal rose from 55 to 85%.The increase in dye degradation can be attributed to a number of factors, including the disintegration of dye molecules, the destruction of dye structures as a result of an increase in energy pressure, and the total decomposition of dye 5,40,47 .Figure 5d depicts the interaction effect of contact time and photocatalyst dose.The duration ranged from 5 to 40 min, and the photocatalyst dose ranged from 25 to 100 mg.The removal percentage rose from 65 to 98% as the photocatalyst dosage increased.The optimal dose for reducing photocatalyst consumption was determined to be 62 mg.In relation to the time variable, the photocatalytic removal rate increased from 5 to 83% between 5 and 22 min, and then decreased from 83 to 75% between 22 and 40 min.Increasing the photocatalyst's contact time with US and UVA lamps initially accelerated the oxidation processes.After 22 to 40 min, the removal rate decreased due to increased competition between the dye molecule and the photocatalyst and the saturation of the active sites 5 .Thus, 22 min was considered the optimal duration.Figure 5e examines the effect of the US power parameter in the range of 30 to 100 W and the photocatalyst dose in the range of 25 to 100 mg.Both parameters increased directly in proportion to the amount of dye removed.www.nature.com/scientificreports/photocatalyst dose was increased from 25 to 100 mg, and when the US power was increased from 30 to 100W.It is due to the high availability of active reaction sites, OH radicals, and electron-hole pairs 8,43,46 .

Mechanism of sonophotocatalytic degradation
To identify reactive active species in the degradation of R195 by the Scendesmus/Fe 3 O 4 /TiO 2 UV/US process, radical trapping experiments with a variety of scavengers were conducted.100 percent (reactor without scavenger) to 86.9 percent (reaction solution with TiO 2 present).This event demonstrates that O 2 molecules were converted into an O 2 •reaction solution, decreasing the effectiveness from one hundred percent to 66.7% 48 .These findings indicate that the sonophotocatalytic process generates •OH, h + , and O 2 •-in the reaction solution 49 .A potential degradation mechanism for the sonophotocatalytic process has been postulated based on the results of the entrapment test and previous research 6 .Using adsorption and photolysis, certain contaminants can be eliminated.Sonolysis and sonophotocatalytic processes can also be utilized to eliminate R195 dye in solution and on a catalyst's surface.During these processes, the heated spot event (resulting from the cavitation effect) can separate water molecules into •OH and H• (Eq.( 25)) 6,22,48 .US radiation, via the sonoluminescence mechanism, produces visible light radiation for the generation of electron/hole pairs in the valence and conduction bands of particles along the same pathway 28 .Under UV radiation, however, Scendesmus/Fe 3 O 4 /TiO 2 nanoparticles generate electron-hole pairs by absorbing light (Eq.( 26)) 50 .In addition to directly degrading the contaminant, the holes in the valence band can decompose H 2 O molecules and hydroxyl ions (OH -) to generate • OH (Eqs.( 27) and ( 28)) 6 .All species generated in the solution and solid phases are capable of transforming pollutants into CO 2 , H 2 O, and biodegradable products (Eq.( 29)) 22 .

Isotherm, kinetcs and thermodinamics model
As depicted in Fig. 6, the Langmuir, Freundlich, Temkin, and Harkins-Jura isotherm adsorption models were implemented.The Freundlich (R 2 = 0.9782), Harkins Jura (R 2 = 0.9438), Temkin (R 2 = 0.9687), and Langmuir (R 2 = 0.9584) models (Table 5) provided a more accurate description of the equilibrium adsorption data.Freundlich's isotherm is an empirical model that depicts photocatalyst-pollutant interactions on heterogeneous surfaces and in multilayer adsorption 5 .With 1/n and K F values of 0.4036 and 12.68 mg1 -n g -1 L -n , respectively, the adsorption process and reaction's intensity were favorable.In addition, the Harkins-Jura model confirmed the adsorption of R195 molecules onto the heterogeneous surface 33 .In contrast, the presence of exothermic and physical adsorption between R195 molecules and Scendesmus, Fe 3 O 4 , and TiO2 was indicated by the positive value of b T (43.266J/mol) in the Temkin isotherm 32 .The optimal adsorption capacity (q m ) predicted by the Langmuir isotherm was close to the experimental value, indicating that the photocatalyst had a uniform surface with the same activation energy 31 .In addition, the R L value between 0 and 1 (R L = 0.0269) indicated that the adsorption procedure was successful.Using pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion kinetic models, the R195 removal mechanism was predicted 5 .According to Fig. 7 and Table 5, the equilibrium condition for R195 removal was stabilized after 60 min for all concentrations tested, ranging from 50 to 500 mg/l, as shown in Fig. 7 and in Table 5.At 300 mg/l of R195, the empirical data were best described by the pseudofirst-order (PFO) model with R 2 = 0.9925.These findings reveal a correlation between the quantity of physical R195 adsorption and the increased driving force responsible for the efficient diffusion of R195 molecules to the surface of Scendesmus/Fe 3 O 4 /TiO 2 and their occupation of the remaining active sites 33 .The pseudo-second-order (PSO) model best described the adsorption process of 100, 200, and 400 mg/l of initial R195 concentrations, with R 2 values of 0.9983, 0.9731, and 0.9722, respectively, when considering chemisorption as the predominant adsorption process with electron donor-acceptor and dispersal interactions 51 .The Elovich model also demonstrated the chemical adsorption of R195 molecules on the solid surfaces of exceedingly heterogeneous adsorbents (R2 > 0.9871) 5 .The intra-particle diffusion model provided the best fit to the adsorption data (Table 5, R 2 = 0.9857 for 50 mg/l R195 and R 2 = 0.9398 for 500 mg/l R195, respectively).Since the relationship between qt and t0.5 is linear, intra-particle diffusion should be the rate-regulating process 35,36 .
As shown in Table 5, the activation energy was calculated to be 69.12kJ mol -1 .The exothermic adsorption mechanism was revealed by the negative standard enthalpy of activation (ΔH o = −23.368) 5 .Moreover, the increasing value of the standard Gibbs free energy of activation (ΔG o ) with increasing temperature demonstrated that the process was not spontaneous 22 .The positive value of standard entropy of activation (ΔS o = + 21.167) was related to the transient molecular configuration at the summit of the energy barrier, indicating an increase in the degree of loss of freedom when the activated complex is formed from the reactants 6,33  Under constant conditions (pH = 5, photocatalyst dosage = 100 mg, initial R195 concentration = 100 mg/l, ultrasound power = 38W, and exposure time = 20 min), the reusability of the synthesized Scendesmus/Fe 3 O 4 /TiO 2 photocatalyst was evaluated (Fig. 8).After five cycles, the photocatalytic efficiency of Scendesmus/Fe 3 O 4 /TiO 2 remained above 95% without any discernible decline.Due to its stability, the synthesized Scendesmus/Fe 3 O 4 / TiO 2 composite is economically viable for use in the effluent treatment process 22 .Future product development and convincing investors and stakeholders could increase the renewability and cost-effectiveness of the final photocatalyst 6 .

Comparison of sonophotocatalytic degradation with other methods
Numerous techniques for degrading textile dyes have been investigated.

Conclusion
In the present investigation, Scendesmus/Fe 3 O 4 /TiO 2 was synthesized as a novel sonophotocatalyst for degrading R195 dye.Diagnostic analyses such as SEM, mapping, FTIR, and VSM confirmed the efficacy of the TiO 2 coating on Scendesmus/Fe 3 O 4 and the resulting photocatalyst.Scendesmus/Fe 3 O 4 /TiO 2 nanoparticles are effective against sonolysis, photolysis, adsorption, and photocatalytic processes when exposed to ultraviolet light and ultrasonic waves.The R195 removal efficiency increases as operating parameters such as photocatalyst dosage, ultrasound power, radiation power, and exposure time are increased, but decreases as initial pH and initial R195 concentration are increased.Under optimal conditions, such as a pH of 5, a photocatalyst dosage of 62.5 mg/l, an exposure duration of 22 min, an initial R195 concentration of 125 mg/m3, and a US power of 65W, the maximum R195 removal was 100%.According to the proposed quadratic model, the concentration of R195 was the most significant variable because of its high F-value.The Freundlich isotherm model and the intra-particle diffusion model best fit the experimental data when taking into account the heterogeneous surface of the photocatalyst and multilayer adsorption.Thermodynamic analysis has confirmed that endothermic and nonspontaneous  www.nature.com/scientificreports/adsorption processes occur.Under repeated irradiation from the United States, the recycled Scendesmus/Fe 3 O 4 / TiO 2 demonstrates exceptional activity and regular stability for pesticide removal.The addition of different scavengers to evaluate the active species of the sonophotocatalytic process revealed that all three species, O 2 , • OH, and h + , were produced during the process and that h + is the active species in the degradation of R195 into CO 2 and H 2 O.The Scendesmus/Fe 3 O 4 /TiO 2 photocatalyst was deemed a novel sonophotocatalyst for the mineralization of R195 based on analyses of various parameters and stability experiments.In conclusion, the transformation of scendesmus into a photocatalyst can not only eliminate the need for additional R195 degradation and reduce the cost of wastewater treatment, but also provide a valuable and efficient photocatalyst at a lower cost than commercial Microalgae that contributes to environmental preservation. https://doi.org/10.1038/s41598-023-45274-1 https://doi.org/10.1038/s41598-023-45274-1 Photocatalyst dosage, mg (B) 25 62.5 100 Exposure time, min (C) 5 22.5 40 Concentarion of dye, mg/lit (D) 50 125 200 US power, W (E) 30 65 100

Figure 4 .
Figure 4.The diagnostics plots for validation of quadratic model: (a) predicted values vs. factual values, (b) normal probability distribution of residuals, (c) internally studentized residuals vs. predicted values plot, (d) internally studentized residuals vs. run numbers, and (e) Box-Cox plot.

Figure 5 .
Figure 5.The three-dimensional interaction effects of pH and concentration of dye (a), pH and photocatalyst dosage (b), pH and US power (c), exposure time and photocatalyst dosage for (d), photocatalyst dosage and US power (e), exposure time and US power (f).

Table 2 .
ANOVA used to the designated quadratic model. Scendesmus/

Table 4 .
Experimental conditions, and the obtained results.

Fe 3 O 4 /TiO 2 recycle
. Scendesmus/Fe 3 O 4 /TiO 2 +))) + UVA → h VB+ + e CB − R195 + active radicals → CO 2 + H 2 O + byproducts Table 6compares these techniques for the degradation of R195.The comparison demonstrates that sonophotocatalysis of R195 using Scendesmus/Fe 3 O 4 / TiO 2 as a photocatalyst yields superior results in comparison to other techniques.According to the obtained data, the present photocatalyst (Scendesmus/Fe 3 O 4 /TiO 2 ) is novel, relatively effective, cost-effective, and broadly accessible.Scendesmus was used as a precursor for the first time in this study to produce a magnetic photocatalyst and eliminate R195 dye.In this investigation, garbage was used as a photocatalyst to remove pollutants from farm effluent.From an ecological standpoint, this matter is of the utmost importance.

Table 5 .
Parameters of isotherm, kinetics and thermodynamics model.

Table 6 .
Comparison with various Methods for the Removal of R195 Dyes.