One-Pot Synthesis of Zinc Oxide Nanoparticle for Bromophenol Blue Adsorption and Its Antifungal Activity Against Filamentous Fungi

Zinc oxide nanoparticles (ZnONP) have gained attention in recent years due to their multifunctional uses, potent adsorptive potential and effective antifungal activities. Despite these desirable characteristics, ZnONP has not been used for the adsorption of bromophenol blue (BRB) and tests as antifungal agents against certain important lamentous fungal strains have been limited. In this research, ZnONP was prepared via a facile one-pot synthetic approach and applied in the adsorption of BRB and as an antifungal agent against the lamentous fungi and plant pathogens; Alternaria alternata CGJM3078, Alternaria alternata CGJM3006 and Fusarium verticilliodes CGJM3823. The ZnONP was characterized by the UV, FTIR, XRD, TGA, BET, SEM, TEM, and EDX techniques, which showed ecient synthesis. The characteristics ZnO UV absorption band was observed at 375 nm, while the XRD showed an average ZnONP crystalline size of 47.2 nm. The SEM and TEM images showed an irregular shaped and aggregated porous structure of 65.3 nm average-sized ZnONPs. The Freundlich, pseudo-second-order, and intra-particle diffusion models showed R 2 > 0.9494 and SSE < 0.7412, thus, exhibited the best t to the isotherm and kinetics of adsorption. Adsorption thermodynamics revealed feasible, endothermic, random, and spontaneous adsorption of BRB onto the synthesized ZnONPs. The antifungal assay conducted, depicted strong antifungal activities against all three tested fungal cultures. A model was proposed on what causes this antifungal effect. This research demonstrated the potent use of ZnONP for the adsorption of BRB and as effective antifungal agents. Zinc oxide nanoparticle (ZnONP) was synthesized in a- simple one-pot system and applied for the adsorption of bromophenol blue (BRB) and as an antifungal agent against Alternaria alternata and Fusarium verticilliodes lamentous fungi. The FTIR showed the presence of the O-H and Zn-O bands on the synthesized ZnONP, which were responsible for the adsorption of BRB via electrostatic, hydrophobic, and weak Vander Waals interaction. The XRD, UV, and EDX characterizations showed the successful synthesis of the ZnONP. Thermal analysis revealed high thermal stability of the ZnONP with a 22.92% weight loss at 800 o C, while BET analysis showed sucient surface area and pore properties desirable for ecient BRB uptake from solution. The SEM and TEM morphology displayed an irregular shaped and aggregated porous structure of ZnONPs. The solution temperature, pH, time, BRB concentration, and ZnONP dosage were found to inuence signicantly the BRB uptake on ZnONP. The operating conditions were selected as pH, temperature, time, dosage, and concentration of 4.0, 300 K, 180 min, 0.1 g, and 50 mg/L respectively. The Freundlich model presented the best t to the isotherm analysis for the adsorption process compared to the Langmuir, Flory Huggins, and Temkin isotherm models. For kinetic analysis of BRB adsorption onto ZnONP, the pseudo-second-order and intra-particle-diffusion were better tted than the Pseudo-rst-order and liquid-lm-diffusion models. A feasible, spontaneous, random, and endothermic removal of BRB onto ZnONP was revealed from the thermodynamic evaluation of the process. The synthesized ZnONP was found to be ecient in the adsorption of BRB from solution with a maximum monolayer uptake capacity of 3.099 mg/g, which was higher than some previously reported adsorbents. In the fungi, A.


Introduction
In recent years, there have been growing concerns arising from the rapid pollution of water bodies around the world 1 . This is attributed to technological advancements resulting in the rapid growth of industries, and subsequently the pollution of water from industrial e uents 2 . Again, agricultural pesticides, fertilizers, and herbicides are easily washed off by running water into receiving water bodies 3 . This water pollution has signi cantly affected aquatic lives, made the water unsafe for drinking, and resulted in several health effects 4,5 . Among several water pollutants, dyes have gained signi cant attention from environmental scientists 6 . This is because dyes are extensively used in the textile, leather, cosmetic, and paper industries 7 . The textile industry alone consumes over 700,000 tons of dyes annually 8,9 . Thus, there is a high amount of dyes in the e uents released from these industries. Apart from that, dyes are allergenic, mutagenic, and carcinogenic at certain concentrations, hazardous, affect photosynthesis in Metallic nanoparticles are known to be promising owing to their e cient adsorptive and catalytic degradation potentials for dye containing water [23][24][25] . In particular, zinc oxide nanoparticle (ZnONP) has received signi cant attention for water treatment because of its nontoxicity, long-term stability, acceptable cost, biocompatibility, and potent antimicrobial activities against microbes frequently encountered in water 26,27 . Thus, a combination of the adsorption potentials and the antimicrobial activities in water treatment would be highly effective to obtain portable water. Therefore, the e cient treatment of dye-polluted water by the use of ZnONPs is well documented 26,28,29 .
However, from a thorough literature search, there is no evidence of the use of ZnONP in the adsorption of BRB from water. Thus, this study evaluated the potentials of ZnONP for the treatment of BRB polluted water.
Several studies have been performed on the antibacterial and antifungal activities of ZnONPs, which proved that ZnONP is a potent antimicrobial agent 27,[30][31][32][33] . However, studies on the antifungal activity of nanoparticles against lamentous fungi are rare 34,35 . In this study the two plant pathogens were studied. The lamentous fungus Alternaria alternata is a pathogen of fruit and vegetables such as strawberries, tangerines, mandarins, grapefruits, and tomatoes, thus causing extensive post-harvest spoilage and loss 36 . The pathogenicity of A. alternata is due to their secretions of host-selective toxins (HST) such as Alternaria alternariol (AAL)-toxin and Alternaria F (AF)-toxin 37 .
Additionally, A. alternata employs cell wall degrading enzymes, such as pectic enzymes, and organic acids 36 that lower the pH and act synergistically with the enzymes to digest Calsium-acetate, which causes damage to the host tissues 36 . In humans, Alternariaalternata are/is associated with hypersensitivity pneumonitis, bronchial asthma, allergic sinusitis, rhinitis, and cutaneous, subcutaneous infections in humans 38 .
The lamentous fungus Fusarium verticilliodes is a seed-borne endophytic pathogen of maize and cereals such as wheat, and can infect a wide variety of other plants worldwide 39 . This fungus is the causative agent for ear rot, kernel rot and seedling blight of maize, and head blight of wheat and therefore largely responsible for pre-and post harvest losses 40 . For humans and animals F. verticilliodes secretes fumonisin B that accumulates in the kernels of maize or wheat, causing toxicity in resulting food commodities 41 . Fumonisin B1 toxin causes nephrotoxic, hepatotxic and cytotoxic effects on the livestock cattle such as lambs 42 . Besides fumonisin, infected seeds in storage conditions are capable of producing moniliformin, zearoleanone and trichothecene that cause up to 20% grain loss 43 and that also represent dangerous mycotoxins 42 . Fusarium mycotoxin adulteration in agricultural commodities poses a global threat to food safety and has substantial economic signi cances. F. verticilliodes outbreaks have been reported in many countries in Asia, New Zealand, Africa, Europe, and South America 44  There is a need to discover novel control agents to prevent plant diseases and post-harvest losses of food crops and grains associated with lamentous fungi, as well as to minimize harmful effects of these fungi on humans and livestock. Although a few studies have reported ZnONP antifungal activities against Alternaria alternata 34,35 , no study was conducted speci cally on these two South African strains (CGJM3078 and CGJM3006) of Alternaria alternata. No antifungal studies with ZnONP were conducted so far against strains of F.verticilliodes. The present study investigated the extent of the antifungal activities of ZnONP against these economically signi cant postharvest fungal pathogens, especially with the particular ZnONP particles developed in this study.
The aim of this study is the evaluation of the adsorptive potentials of ZnONP for BRB dye as well as its antifungal activity against A. alternata and F. verticilliodes. The ZnONP was synthesized by a simple traditional one-pot chemical reduction approach and characterized. The synthesized ZnONP was utilized for BRB adsorption at changing pH, dye concentration, material dosage, temperature, and time. The thermodynamics, kinetics, and isotherm of the adsorption process were evaluated for a proper understanding of the dye adsorption process. Finally, the antifungal activity of the synthesized ZnONP against A. alternata and F. verticilliodes was investigated in-vitro, and a possible mechanism of action against these fungi is proposed.

Synthesis of ZnONP
A simple one-pot synthesis via chemical reduction was utilized for the preparation of ZnONP 46 . Herein, 4.0 g of zinc acetate was added to 100 mL of distilled water in a beaker. The solution was stirred with a magnetic stirrer on a hot plate at 30 o C for 40 min. This was followed by the dropwise addition of 0.2 M NaOH to the solution with continuous stirring until the pH was 11.0. The solution became white due to the precipitation of ZnO and was stirred further for 1 h, after which it was allowed to stand for 50 min. The ltrate was decanted and the synthesized ZnONP was washed repeatedly with excess distilled water until neutral pH and nally with ethanol. The prepared ZnONP was dried in an oven at 250 o C for 5 h. The as-prepared nano-sorbent was stored in an airtight sample container and kept in a desiccator until use.

Characterization of the synthesized ZnONP
The ZnONP was characterized to evaluate the surface properties necessary for e cient adsorption of BRB from water. The eld emission scanning electron microscopy (FE-SEM; Jeol model) was used to examine the particle size and morphology, while the Energy-dispersive X-ray spectroscopy (EDS; Oxford model) coupled to the SEM instrument was used to determine the elemental composition. The morphology and surface structure was further analyzed with the Transmission electron microscopy (TEM) (Philips-FEI-CM100 model) equipped with a Mega View III digital camera. The functional groups of ZnONP were examined by the Fourier transform infrared (FTIR) spectroscopy (FTIR; Bruker Tensor 27 model). The crystalline phases were identi ed by the X-ray diffractometer (XRD; Brucker model) with Cu radiation of 1.5 Å at the 2-theta range of 10 -80 o . The pH drift method was used to evaluate the pH point of zero charge (pHpzc) as described elsewhere 47 . The absorption spectrum of the ZnONP was obtained using distilled water as a reference with the UV-Spectrophotometer (Shimadzu UV-1800 model) in the range 250 to 850 nm. Thermal stability was analyzed by the thermo-gravimetric analyzer (TGA; Mettler Toledo Model). The surface area analyzer (Micrometrics ASAP 2020 model) was used to examine the Surface area (S BET ) and pore properties and the results were re ned by the MicroActive VI.01 software. The pH of the solution was adjusted from 2.0 to 9.0 using 0.1 M NaOH and HCl. Batch adsorption was applied to determine the in uence of solution pH, ZnONP dosage, BRB concentration, sonication time, and temperature at the operating conditions presented in Table 1. Batch BRB adsorption was carried out by adding a given amount of ZnONP to 10 mL of a given BRB concentration at the speci ed pH. The mixture was sonicated at a particular temperature in an ultrasonic 2.5 L water-lled bath at the speci ed time. At the end of the given time, the solution was centrifuged at 8000 rpm for 30 min, and the ltrate was analyzed for residual BRB at a maximum wavelength of 590 nm, using the UV Spectrophotometer (Shimadzu UV-1800 model). The percentage adsorption and uptake capacity q e (mg/g) were calculated from the percentage removal and mass balance equations, respectively 8 : Where C e and C o in mg/L are the nal and initial concentrations of BRB in solution, respectively. m (g) is the mass of ZnONP used and V (L) is the volume of BRB solution used.

Isotherm, kinetic and thermodynamics of adsorption
The isotherm modeling on the adsorption of BRB onto ZnONP was evaluated from the Freundlich, Temkin, Langmuir, and Flory-Huggins models 12 . The adsorption kinetics was deduced from the pseudo-rst-order (PFO), pseudosecond-order (PSO), liquid lm diffusion (LFD), and intraparticle diffusion (IPD) rate models, while thermodynamics was deduced from Van't Hoff's equation 48 . The equation and symbols of the isotherm, kinetics, and thermodynamics are described in the supplementary information.

Statistical analysis
Each experiment was done in duplicate and the average value was computed. The error bars in the gures indicate the standard deviation from the mean. The statistical function of the origin 2019b software was used to determine the sum square error (SSE) and the coe cient of determination (R 2 ), used to analyze the best-tted isotherm or kinetic model.

Antifungal analysis
The in-vitro antimicrobial activities of the ZnONP were tested against the three fungal strains, viz A. alternata CGJM3078 served as the positive control while sterile distilled water was used as the negative control for all the experiments.
Plates were incubated at room temperature in the upright position until zones of inhibition were observed, which was considered an endpoint parameter for the antimicrobial activities. The diameter of the inhibition zones was measured using the Image J software program (https://imagej.nih.gov/ij/) as per a previous study 50 . All the culture media were procured from Sigma Aldrich, Merck KGaA, Darmstadt, Germany, and Neogen Culture media, Heywood, UK respectively.

Results And Discussion
Characterization of ZnONP The XRD characterization used to examine the crystalline phases of ZnONP is shown in Fig. 1a The FTIR spectra of ZnONP before and after the adsorption of BRB is shown in Fig. 1b. The spectra help to identify the functional groups present on ZnONP. The band at 3369 cm -1 corresponds to the O-H stretching vibration, while the O=C=O functionality of absorbed CO 2 on the ZnONP was depicted by the bands at 2162 cm -1 and 2008 cm -1 53 .
The absorption band at 1380 cm -1 corresponds to the OH bending of water acquire from the absorption of moisture from air 26 . Also, the Zn-O stretching vibrations were indicated by the bands at 887 cm -1 and 550 cm -1 , which con rms the successful synthesis of the ZnONP. After the adsorption of dye, the BRB-loaded ZnONP showed shifts in absorption bands from 3369 to 3377 cm -1 and 1380 to 1330 cm -1 for OH, from 2008 to 2033 cm -1 for the O=C=O, and from 550 to 557 cm -1 for the Zn-O functionalities. This indicated the involvement of the OH and Zn-O groups in the uptake of BRB on the adsorbent and that the mechanism of BRB uptake on ZnONP could be attributed to electrostatic interactions, H-bonding as well as weak Vander Waals interaction 46 .
The UV spectrum of the as-prepared ZnONP is shown in Fig. 1c. The nitrogen adsorption-desorption isotherm (Fig. 1e) of the ZnONP as obtained from BET analysis revealed a surface area of 9.259 m 2 /g and correlated with type III isotherm according to the IUPAC classi cation 46 . Also, the pore characteristics (Fig. 1f) as obtained from the Barret-Joyner-Halenda (BJH) method showed a pore volume of 0.037453 cm 3 /g and an average pore diameter of 9.87 nm indicating the mesoporous structure. Although the surface area of our as-prepared adsorbent was, lower than 26.78 m 2 /g obtained from the hydrothermal synthesis of ZnONP used in the adsorption of heavy metals 26 , the mesoporous structure (see discussion in the next paragraph) would be highly in uential for the e cient removal of dye molecules from solution 55 .
The SEM images of the as-prepared ZnONP are shown in Fig. 2a and Fig. 2b. As observed, the ZnONP adsorbent is associated with an irregular surface structure, particle aggregation, with a highly porous morphology, which corroborates the porosity measurements. The average ZnONP size of 65.3 nm was obtained from the SEM structure. Again, the porous structure of the synthesized ZnONP would ensure easy diffusion of dyes molecules favoring e cient adsorption of the pollutant from solution 56 . The agglomerated characteristics of the synthesized ZnONP was further veri ed from the TEM image (Fig. 2c). Besides, the EDX spectra (Fig. 2d) of the adsorbent, showed 78.9% zinc and 21.1% oxygen, which further con rms the successful synthesis of the ZnONP. The absence of other elements also indicates a pure synthesized ZnONP, which corroborates the results of the XRD analysis. A similar nding was also reported by other workers 26,57,58 . The absence of impurities in the synthesized ZnONP is important for e cient antimicrobial activity 58 .

BRB uptake on ZnONP
Several operating parameters such as the temperature of the solution, dye concentration, solution pH, time, and material dosage are known to in uence the overall uptake of pollutants onto adsorbent materials 17,59,60 . Thus, we investigated the effect of these parameters on the uptake of BRB onto ZnONP. Fig. 3a illustrates the in uence of pH on dye removal from solution onto the as-prepared particle. A steady decrease in the adsorbent's adsorption capacity and percentage uptake of BRB from pH 2.0 to 6.0 was obtained after which a slight increase up to pH 9.0 was observed. This trend is strongly dependent on the pHpzc of ZnONP as well as the pKa of BRB dye in solution. The pHpzc of the synthesized ZnONP was 6.3 while BRB has a pKa value of 3.84 8 . Thus, ZnONP is associated with a positive surface charge at pH values below 6.3 but becomes negative above this pH. Also, BRB exists as negatively charged molecules below 3.84 after which it becomes neutral and then exists as positively charged species as pH increases. Thus the optimum uptake achieved at pH values below 4.0 was due to strong electrostatic attraction between the positive ZnONP surface and the anionic BRB species in solution. Again, the slight increase observed from pH 6.0 to 9.0 is probably due to the attraction between positively charged BRB species in solution and the negatively charged adsorbent surface. Although optimum BRB removal was obtained at pH 2.0, this pH is too acidic to be associated with real dye-polluted wastewaters. Therefore, we selected pH 4.0 for subsequent experiments due to its closer association with real dye polluted water and the higher uptake recorded compared to values from pH 5.0 to 9.0.
The in uence of the initial concentration of dye on the removal of BRB onto ZnONP is shown in Fig. 3b.   Fig. 3e. With an increase in solution temperature from 300 to 323 K, an increase in ZnONP adsorption capacity from 50.6 to 64.8%, and percentage adsorption of BRB from 2.53 to 3.24 mg/g were achieved. This suggests that the uptake of BRB on ZnONP is likely an endothermic one since it is favored at higher temperatures.
The improved BRB uptake at higher temperatures could be attributed to enhanced interaction between the BRB species in solution and the adsorption sites of ZnONP prompted by higher kinetic energy overcoming mass transfer resistances 68 . A similar nding was also documented in the uptake of As (III) from solution on ZnO nanorods 28 .

Isotherm analysis of BRB adsorption
The adsorption isotherm modeling of BRB adsorption on the as-prepared ZnONP was conducted to obtain useful information on the favorability of the adsorption process, nature of adsorption as well as potent interaction between the two phases 56 . This was analyzed by the Langmuir, Temkin, Freundlich, and Flory-Huggins models as illustrated in Fig. 4. The calculated isotherm parameters obtained from the modeling are presented in Table 2. The best model t was judged by the closer the R 2 value is to one and the smaller SSE. The Langmuir model, which depicts a monolayer dye uptake on a homogenous material surface 48 , presented a lower R 2 and higher SSE than the Freundlich model and thus was not applicable in the description of BRB adsorption onto ZnONP. The  Table 2, the n value was 2.304, which indicated e cient interaction between BRB species in solution and the ZnONP adsorbent. The favorability of the dye adsorption process was further tested by the application of the Langmuir separation factor [R L = (1/1 + K L C o )] 65 . Where K L is the Langmuir equilibrium adsorption constant 70 . The R L value denotes a linear (R L = 1), an irreversible (R L = 0), a favorable (0< R L <1) and unfavorable (R L >1) removal process 28 . The R L value for BRB removal on ZnONP was in the range of 0.115 to 0.394, which corroborates the favorable adsorption of BRB, indicating that ZnONP is a viable adsorbent for the treatment of BRB polluted water. Besides, the monolayer uptake capacity of ZnONP for BRB was 3.099 mg/g, which is higher than that of activated charcoal (0.081 mg/g) 73 and polymeric gel (2.99 mg/g) 74 but lower than 22.72 mg/g obtained for chitin nanoparticle 75 . Thus, the simple preparation procedure as well as potent antifungal properties (see discussion in the "Antifungal activity" section) would be the advantage in the application of ZnONP for BRB wastewater treatment.

Kinetics and thermodynamics of adsorption
The kinetic modeling of adsorption processes helps in the calculation of kinetic parameters, which is useful in system design and provides useful information on sorption mechanism 76 . The kinetics of BRB adsorption onto ZnONP was modeled by the PFO, PSO, LFD, and IPD equations. The kinetic plots are presented in Fig. 5 while the obtained kinetic parameters are given in Table 3. It is obvious from the R 2 of 0.9495 and the SSE of 0.7411 that the PSO was more suited than the PFO model in the kinetic description of BRB uptake onto ZnONP. This was also supported by the closer calculated qe (3.0597 mg/g) of the PSO to the experimental qe (2.53 mg/g), than that presented by the PFO model (3.4883 mg/g). The best t presented by the PSO models suggests the involvement of electrostatic interactions between the BRB molecules in solution and ZnONP adsorbent in the dye removal process 77,78 . This implication corroborates our deduction from the FTIR analysis obtained after BRB adsorption onto ZnONP, which showed the involvement of electrostatic interactions. A similar result was reported in the adsorption of methylene blue onto ZnONP impregnated sawdust based cellulose nanocrystals 79 .
Furthermore, the LFD and IPD models provide reliable information about the diffusion mechanism of adsorption 56 .
Comparing the two diffusion models, it is evident that the IPD model was best tted to the diffusion process of BRB molecules onto ZnONP as inferred from the high R 2 (0.9889) and low SSE (0.0581). This indicates that the diffusion of BRB through the surface pores of ZnONP played a vital role in the overall adsorption process than the boundary layer diffusion. However, the occurrence of the intercept (0.1215), showed that particle diffusion was not solely responsible for BRB uptake, but to some extent involves lm diffusion 29,48 . A similar nding in the adsorption of BRB onto Solanum tuberosum peel -silver nanoparticle hybrid was reported in our previous work 8 . The ultra-sonication applied prompted potent interaction between the dye species and the particle pores thus enhancing the particle diffusion mechanism. In addition, this observation is in line with the pore and SEM analysis, which showed a porous nature of ZnONP that, would enhance the dye uptake from the solution. The thermodynamics of BRB adsorption on ZnONP was also evaluated from the Van't Hoff plot as illustrated in Fig.   5e. The calculated thermodynamic parameters such as the changes in enthalpy (∆H o ), entropy (∆S o ), and free energy (∆G o ) were used to analyze the spontaneity, randomness, and the physical or chemical nature of BRB uptake onto the synthesized ZnONP 80 . The thermodynamic parameters obtained are presented in Table 4. obtained for the removal was slightly higher than the physisorption range but far lower than the chemisorption range. This indicated physicochemical adsorption of BRB onto ZnONP rather than a purely chemical or physical uptake, dominated mainly by the physical forces of adsorption 85 . Again, this implies that a much lower energy barrier is to be overcome in the desorption of the BRB loaded ZnONP during the regeneration of the adsorbent, compared to adsorption processes dominated or controlled by chemisorption. Furthermore, the increasing randomness at the ZnONP-BRB solution interface was indicated by the positive ∆S o value of 74.02 J/molK 86 . This increasing random interaction at the interface must have enhanced e cient interaction between BRB molecules and the particle pores of ZnONP, which accounted for the dominant role played by intraparticle diffusion in the overall adsorption process.

Antifungal activity
The antifungal activity of the ZnONP is tested for possible application as simultaneous BRB removal and antifungal of wastewater. Noticeably, as shown in Fig. 6, all of the tested concentrations of ZnONP showed inhibitory effects on the three cultures, and the zones of inhibition increased consistently as the concentration of ZnONP increased ( Signi cantly less volumes of ZnONP (40 µL) were used against all the tested fungi in this study in comparison to a previous study 32 , where 100 µL volume was implemented for an identical concentrations range (0.002 -5 mg/mL). The enhanced antifungal e ciency of the formulated ZnONP in the current study is possibly based on factors such as the size and shape of the particles, a large surface area to volume ratio that improved the solubility of the nanoparticles in comparison to the larger ones, the generation of reactive oxygen species (ROS) and the effective release of Zn 2+ ions 50 . The exact underlying molecular mechanisms of ZnONP antifungal activities are yet to be elucidated 90 . In this study we proposed a few plausible mechanisms (Fig. 7). Zn 2+ can possibly be released from the surface of ZnONP, as it has been shown in AgNPs 91 that interacted with the fungal cell wall, passed and accumulated in the cytoplasm. This causes cell metabolism disturbances, impairment of the nucleic acid material by their irreversible adherence, ribosome disassembly, protein denaturations, electron chain disruptions, all of which ultimately resulting in cell death (Fig. 7). The interactions may also cause deformed fungal hyphae with ruptures and unusual bulging as was observed in an SEM study of antifungal activities of Zn compounds against pathogenic fungal strains of Fusarium graminearum, Penicillium citrinum and Aspergillus avus 92 . The generation of the reactive oxygen species (ROS) ( Fig. 7) as per a previous study 50 , can cause lipid peroxidation, leading to cell death. Simultaneously, the fungal cell wall can become more permeable because of the Zn 2+ , resulting in subsequent leakage of the plasma uid and cellular organelles causing cellular senescence (Fig. 7). SEM structure imaging of the ZnONP developed in the present study revealed the average size of ZnONP as 65.3 nm. This is consistent with the previous ndings 30 , where the average size was reported as 70 ± 15 nm. Those ZnONPs successfully inhibited the growth of mycotoxin producing fungi, Botrytis cinerea and Penicillium expansum, causing cellular perturbations, and fungal hyphal distortion.

Conclusions
Zinc oxide nanoparticle (ZnONP) was synthesized in a-simple one-pot system and applied for the adsorption of bromophenol blue (BRB) and as an antifungal agent against Alternaria alternata and Fusarium verticilliodes lamentous fungi. The FTIR showed the presence of the O-H and Zn-O bands on the synthesized ZnONP, which were responsible for the adsorption of BRB via electrostatic, hydrophobic, and weak Vander Waals interaction. The XRD, UV, and EDX characterizations showed the successful synthesis of the ZnONP. Thermal analysis revealed high thermal stability of the ZnONP with a 22.92% weight loss at 800 o C, while BET analysis showed su cient surface area and pore properties desirable for e cient BRB uptake from solution. The SEM and TEM morphology displayed an irregular shaped and aggregated porous structure of ZnONPs. The solution temperature, pH, time, BRB concentration, and ZnONP dosage were found to in uence signi cantly the BRB uptake on ZnONP. The operating conditions were selected as pH, temperature, time, dosage, and concentration of 4.0, 300 K, 180 min, 0.1 g, and 50 mg/L respectively. The Freundlich model presented the best t to the isotherm analysis for the adsorption process compared to the Langmuir, Flory Huggins, and Temkin isotherm models. For kinetic analysis of BRB adsorption onto ZnONP, the pseudo-second-order and intra-particle-diffusion were better tted than the Pseudo-rst-order and liquidlm-diffusion models. A feasible, spontaneous, random, and endothermic removal of BRB onto ZnONP was revealed from the thermodynamic evaluation of the process. The synthesized ZnONP was found to be e cient in the adsorption of BRB from solution with a maximum monolayer uptake capacity of 3.099 mg/g, which was higher than some previously reported adsorbents.
In addition, the prepared ZnONP exhibited potent antifungal activities against the lamentous fungi, A. alternata and F. verticilliodes. The antifungal effects, such as inhibition of growth and reproduction of the lamentous fungi, are enhanced signi cantly with the ZnO nanostructures. Therefore, the present study, together with previous studies, showed that ZnONP have tremendous potential as an effective postharvest disease control antifungal agents against lamentous fungi, or even possibly in the eld. No studies have, however, tested this in vivo.