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Oct 18, 2024

Novel antifouling paint formulation based on Ca2​Cr2O5​ and CaMnO3​ NPs as a protective pigment | Scientific Reports

Scientific Reports volume 14, Article number: 24474 (2024) Cite this article Metrics details This work focused on the preparation of novel antifouling paint based on Ca2Cr2O5 and CaMnO3 NPs as a safe

Scientific Reports volume 14, Article number: 24474 (2024) Cite this article

Metrics details

This work focused on the preparation of novel antifouling paint based on Ca2Cr2O5 and CaMnO3 NPs as a safe protective pigment which were replaced with cuprous oxide. Three paint formulations were prepared for comparison, a blank formula without an antifouling agent (F1), a commercial antifouling formula based on 100% cuprous oxide as an antifouling agent (F2), and AF formula based on 75% Ca2Cr2O5 and CaMnO3 NPs and 25% Cu2O. The high performance and durability of the paints based on the prepared pigments were evident from their impact resistance, adhesion, pending, hardness, and chemical resistance, which were compared to the blank formula (F1). The corrosion resistance of the painted films was also investigated using the salt spray test method, and the results were promising compared to the blank and standard formulations. All painted steel plates were exposed to seawater through field tests in the Suez Canal at Port Said for up to 6 months. The results showed that the paints based on F2 and F3a, b enhanced the antifouling activity through six months of exposure. The obtained results demonstrated greater efficiency of the painted steel-based F3a than F1 and F3b, and being comparable to the standard formula (F2).

The undesirable growth of microbes, algae, and crustaceans on submerged, exposed substrates is known as marine biofouling. Both dynamic and static structures are severely impacted by fouling (vessel speed reduction, increased fuel consumption, increased hull maintenance, etc.). Many techniques have been employed in the lengthy history of fouling avoidance, including copper sheathing, pitch, and tar. Therefore, to protect coated surfaces from marine microorganisms, paint formulas that have historically included biocidal species are employed1,2.

The goal of antifouling is to inhibit or stop the growth of organisms on underwater surfaces. Antifouling agents prevent pollutants from adhering to surfaces, eliminate microorganisms that come into contact with the surface, and stop the growth of microorganisms and the creation of biofilms. A subclass of antifouling materials with biocidal properties is known as an antimicrobial or antibacterial agent. Much research has been done on materials with antifouling and antibacterial qualities in order to develop antifouling surfaces for biomedical implants and devices3,4.

The earliest antifouling paints date back to the mid-19th century and were made with toxicants like some metals such as Cu2O, dissolved in shellac or drying oil. However, tributyltin (TBT)-based antifouling paints have proven to be the most effective antifouling paints in terms of long-term efficacy. Since January 1, 2008, these TBT-based products have been completely banned due to environmental concerns. In the past ten years, modified coatings-based polymer matrices occasionally combined with rosin—and different types of biocides that come into contact with fouling organisms have emerged as contemporary antifouling solutions5. These consist of mineral substances like cuprous oxide and, less frequently, cuprous thiocyanate, as well as chemical molecules known as booster biocides. In general, booster biocides are toxic to aquatic life6. The two most common active ingredients in modern antifouling coatings are natural biocides and cuprous oxide. Because cuprous oxide is prone to bioaccumulation, it should always be replaced by more environmentally friendly mixtures. Conversely, cuprous oxide is not only an antifouling agent; it is also an essential component in the antifouling coating’s leaching and surface finishing processes. Sr, Ca, Zn, and Mg peroxides are assessed for use as pigments in antifouling coatings. Highly saltwater-soluble metal ions and H2O2 are produced when the oxidizing agents react with seawater7,8. In the marine industry, biofouling is a persistent issue that calls for substantial financial resources for control and novel cleaning techniques. The production of environmentally acceptable, low-toxicity, and harmless antifouling compounds is urgently needed for maritime firms and underwater equipment, as marine coatings based on trichlorophenol (TBT) were outlawed worldwide in 20089. Creating a formula based on natural substances or new biocides (like medetomidine and econea) would be another antifouling tactic6,10,11. Bellotti et al. have demonstrated the potential of zinc “tannate” antifouling paints; nevertheless, antifouling efficacy depended on the formulation, as the antifouling activity was altered by the matrix and plasticizer used12. Antibacterial properties are exhibited by several inorganic nanoparticles based on some metal oxides. Their mechanism includes the release of metal ions (Ag and Cu) and the generation of active oxidative stress (TiO2 and ZnO) in response to UV radiation13,14. It is particularly desirable to have membrane surfaces with multiple defensive mechanisms because of the variety and complexity of membrane fouling. It may be possible to stop biofilm growth and fouling with one of the most promising materials for modifying membrane surfaces. NPs and polymers provide microbial and fouling resistance properties, respectively, and polymer nanocomposites have been produced15,16. Self-polishing copolymer (SPC) coatings remain the most widely used commercial antifouling products. However, they are now mainly made of copper acrylate. These coatings function similarly to the efficient copper-based TBT coatings, offering an acrylate copolymer that hydrolyzes quickly and refreshes the surface, as well as a leaching element for hydrolysis. The potential for continually employing copper has expanded recently with the emergence of copper pyrithione and the development of copper NPs17. Because copper relied on a comparable mode of action for biocide release and offered a similar level of effectiveness in a variety of settings, it was able to replace TBT. Most of the potential mechanisms for copper’s antibacterial effect have to do with either disrupting or penetrating a cell membrane18,19,20,21. By manipulating its size and shape, copper’s antifouling activity can be adjusted. The distinctions between copper’s nano, micro, and macro forms were examined by Chapman et al.21. They discovered that the coatings on copper nanoparticles (NPs) absorbed the least amount of protein, carbs, and slime when suspended in either a sol-gel or polydimethylsiloxane (PDMS), followed by microparticles and, finally, bulk copper22. Fe, Cr, and Co-metal complexes based on hydroxy acetophenone benzoyl hydrazone were reported to have antimicrobial and antifouling properties. By submerging the coated films in seawater, the produced metal complexes combined with epoxy resin were tested for durability, antibacterial activity, and antifouling properties. The results showed that Fe, Cr, and Co-metal complexes might be used as antifouling materials23.

Various heterocyclic compounds were prepared and tested for their biological activity against macrobiofoulants and their suitability as environmentally friendly biocides in a particular kind of self-polishing paint that contained no tin. The findings demonstrated that the prepared compounds’ biocidal, antimicrobial, and antifouling activities were highly significant, suggesting that they could be employed as antifouling agents24. The design techniques and advancements of chemically hybridized polymer–ceramic hybrid antifouling coatings, including a step-by-step hybrid strategy and a one-step sol-gel hybrid strategy, were presented. Moreover, the mechanical and antifouling properties of stereoscopic polysiloxane structures are explored. It looked at what percentage of organic and inorganic components, as well as how crosslinking was done, could indicate the next generation of protective antifouling coatings25. The formulation of rosin paint against marine microorganisms using mixed metal oxide nanoparticles is examined for the first time. After that, they are tested and added to an antifouling paint. We will look at a preliminary assessment of the interest in focusing on microfouling to achieve effective paint.

All chemicals and reagents used in the experiment were of analytical grade. It is unnecessary to purify these chemicals further before use since they could be used as received from the supplier, which were obtained from multiple chemical companies (Merck, Alpha Chem, Fluka, Loba, and El Nasr Company, respectively).

Calcium–chrome, and calcium–manganese oxides, (Ca2Cr2O5 and CaMnO3), were prepared by using the co-precipitation method. A solution of calcium carbonate (CaCO3), chromium carbonate (Cr2(CO3)3) in a calculated 1:1 molar ratio, was prepared. Drops of dilute nitric acid (HNO3) were added to reach complete dissolution and clear solution. A slight amount of residual contaminants was removed by filtration. Then the filtrates were added slowly to a magnetically stirred solution of ammonium carbonate ((NH4)2CO3). Upon addition of the salt solutions, various precipitates with different colors are formed. After complete additions of the salt solutions, the stirring was continued additional time to ensure of complete precipitation and homogeneity of the products. Then the precipitates were filtered out of the residual solution and dried. The dried precipitate of mixed-phase carbonates was then fired at 900 0C to give Ca2Cr2O5. The same procedure was applied for synthesizing CaMnO326,27.

The phase compositions and bond structures of various prepared samples were determined from the X-ray diffractograms (XRDs) utilizing X-ray diffraction analysis (XRD) data using a (Bruker D8 advance instrument, Germany). Copper Kα radiation with a wavelength of 1.54 Å was used over a 2θ range of 20°–80° at room temperature. Fourier transform infrared (FTIR) spectra were recorded on (Bruker, Vector 22 single-beam spectrometer, Germany) with a resolution of 4 cm−1. The samples were ground with KBr (in a 1:100 ratio) to form tablets, which were then mounted in the spectrometer’s sample holder. Measurements were recorded at room temperature in the range of 400–4000 cm−1. Chemical compositions of selected powder samples were analyzed using an ICP instrument (Leeman Labs Inc., Profile Plus 2004, USA). A scanning electron microscope (SEM, JEOL JSM-T 330 A) with an acceleration voltage of 30 kV was used to study the morphology of the precipitated powders. The prepared pigments were evaluated for their oil absorption (ASTM D281-12(2021), hydrogen ion concentration (pH value) (ASTM D1293-12), bleeding of pigments, ASTM D279-02(2019), degree of fineness: ASTM D1210-05(2022), moisture content: ASTM D2216-19, and loss on ignition (ASTM D7348-21).

The same concentration of each of the Ca2Cr2O5 and CaMnO3 NPs were prepared. Tested concentrations were 100–10,000 mg/L for each one at different time intervals: 0 times, 24 h, 48 h, 72 h, and 96 h.

Samples of adult Brachidontes variabilis marine mussels were taken from the waters of the Suez Gulf at Attaqah Mountain. The collected mussels were maintained in 70 cm × 40 cm × 40 cm glass aquariums filled with seawater. Constant aeration, twice-weekly water changes, and occasional removal of dead bivalves were provided. In each experiment, adult mussels ranging in size from 0.5 cm to 1.0 cm were employed.

Ten mussels were used in each test, and the test materials were added to 1-litre beakers containing 500 millilitres of saltwater to reach final concentrations of 100–10,000 mg/L. The same procedures were followed when applying control samples. However, no chemicals were examined28,29.

The paints were prepared using a high-steering mixer at the beginning of the procedure, followed by using a laboratory ball mill to incorporate the prepared pigment NPs and other solid materials. Preparation of the paint formulations were based on gum rosin and vinyl resin as binders, with prepared mixed metal oxide NPs and/or cuprous oxide as antifouling pigments. The formulations also included additives such as a dispersing agent, plasticizer, and epoxy (low molecular weight as additive) to create a tin-free antifouling paint formulation, using the same procedure as for the preparation of the blank sample (F), according to the pigment volume concentration, P/B:2:1. The paints were then applied to steel and glass panels using a brush. All efforts were made to maintain a uniform film thickness of 100 ± 5 μm. The composition of the paint formulations is tabulated in Tables 1, 2, 324.

Four panels, each measuring 25 cm by 40 cm by 1 mm, were prepared for testing; one will be utilized as a blank and the other as a test panel. After oil and grease were removed using solvent cleaning as per SSPC-SP1, the panels underwent abrasive blasting according to ISO 8501-1 to achieve a Sa 2.5 finish. The surface roughness, measured with the Micrometer Elcometer 124 and the Replica Tape Elcometer 122, was 75 μm. The surface was roughened using sandpaper. The panels were then cleaned with fresh water and painted with 100 ± 5 μm of the prepared AF paint29.

The paint films underwent a range of mechanical and physical analyses. Steel panels were prepared according to ASTM D609-17. Film thickness was measured using ASTM D1005-13. Film hardness was determined using a pencil hardness tester following ASTM D3363-11, and specular gloss measurements were carried out according to ASTM D523-18. Flexibility was assessed using ASTM D522-17, and adhesion was tested with a cross-hatch cutter following ASTM D3359-17. The resistance of organic coatings to rapid deformation (impact) was evaluated using ASTM D2794-93 (Reissued in 2001). Corrosion resistance was tested according to ASTM B117-19.

The prepared mixed metal oxide NPs were confirmed by FTIR and XRD, according to our previous work, and the figures of FTIR are presented in Figs. 1 and 2, and Tables 4 and 526,27.

Infrared spectra provided information on the nature of the bonding structures in the prepared mixed oxide samples. Tables 4 and 5, summarize the data obtained from FTIR spectra analysis of the synthesized sample products. The obtained infrared spectrum from CaCO3 (Tables 4 and 5) revealed the presence of very strong absorption band at 1425 cm−1 which corresponding to υ3 and strong absorption band at 874 cm−1 attributed to υ2 symmetric vibration of CO3 and a characteristic absorption band at 707 cm−1 for υ4 asymmetric vibrations of CO3. In addition, the broad absorption bands averaged at 3435 cm−1 and the very weak band at 1642 cm−1 are assigned to the stretching and bending vibration of H2O, respectively. It is worth mentioning that the two absorption bands which are characteristic of H2O are detected in all infrared spectra of the products. The disappearance of the vibrational absorptions is characteristic of the carbonate ions at 1450, 1395 and 1348 cm−1 ; and 890–820 cm−1 corresponding to υ2 and υ4 (symmetric and asymmetric) for CaCO3, MnCO3 and Cr2(CO3)3, respectively. New spectra absorption bands that appear to be associated with newly formed species consistent with this is the appearance of new absorption bands at 1427, 1045, 576, and 429 cm−1 due to different modes of M-O (M = Ca, Mn). The absorption bands at 8,91,639 and 578 cm−1, as shown in Table 5, of Ca2Cr2O5, can also be ascribed to M-O bonds (M = Ca, Cr)27.

FT-IR of CaMnO3, and corresponding CaCO3, MnCO326.

FT-IR of Ca2Cr2O5, and corresponding CaCO3, Cr2(CO)3,26.

Phase identification and crystal structure

Understanding the crystal structure and phase purity of CaMnO3 and Ca2Cr2O5 are crucial for optimizing its performance in various applications. X-ray diffraction (XRD) is one of the primary techniques used to analyze the crystallographic structure of materials like CaMnO3., and Ca2Cr2O5. Once synthesized, the sample is ground into a fine powder to ensure uniformity and then placed in an XRD instrument. The XRD pattern is obtained by directing X-rays onto the sample and measuring the intensity of diffracted rays as a function of angle (2θ). The intensity and position of these peaks can be compared with standard reference patterns from databases such as the Joint Committee on Powder Diffraction Standards (JCPDS). A well-defined set of sharp peaks indicates high crystallinity and phase purity, while broad or additional peaks may suggest impurities or secondary phases.

Figure 3 shows the X-ray diffraction pattern of the prepared MMO sample from calcination at 900 °C for 2 h of the precursors obtained from co-precipitation of CaCO3 and MnCO3 powders. Copper Kα radiation with a wavelength of 1.54 Å was used over a 2θ range of 20–80° at room temperature. It reveals the formation of a perovskite structure. All XRD peaks are assigned to the calcium manganese oxide (CaMnO3) phase and have a high crystalline structure and high compatibility with (JCPDS #50-1746). So, based on the data available from JCPDS card the comprehensive analysis reveals that the significant 2-theta values for XRD analysis of CaMnO3 include those at approximately: 2θ = 25°, 35°, 43°, 50°, 55°, 362°, and 73°. which correspond to Miller Indices in (101), (200), (022), (040), (222), (042) and (242), planes, respectively. The crystal lattice structure constant was found in good agreement with the standard reported.

XRD patterns of the prepared CaMnO3 mixed oxide26.

Figure 4 shows the XRD pattern of the prepared Cr2(CO3)3. All XRD peaks are assigned to the dicalcium dichromium oxide phase and have a high crystalline structure and high compatibility with JCPDS (48–0791) card. From JCPDS card 48–0791, we can extract several key 2-theta values associated with Ca2Cr2O5. These values represent angles at which constructive interference occurs due to X-ray scattering from different planes within the crystalline structure. The data available from JCPDS card 48–0791, here are some notable 2-theta values for Ca2Cr2O5: 2-theta values for XRD analysis of Ca2Cr2O5 include those at approximately: 2θ = 20°, 25°, 33°, 35°, 37°, 39°, 49°, 52°, 58°, 63°, and 65°. which are correspond to Miller Indices in (030), (040), (200), (141), (051), (032), (260), (062), (341), (360), and (100) planes, respectively. The crystal lattice structure constant was found in good agreement with the standard reported30,31,32,33,34,35.

XRD diffraction patterns of Ca2Cr2O5 mixed oxide26.

Figure 5a,b show the SEM images of the precipitated powder samples. Figure 4a,b shows the SEM image of the CaMnO3 sample which appears as spherical in nature and the spherical particles of good hiding power to other surfaces. Whereas the porous structure of the spheres is good for absorption of oil. The size of the particles is in the range of nano size. The spherical structure of the prepared samples increased the oil absorption percentage which is an important factor for oil absorption for computability with bined in the paint formulation.

The SEM images of (a) Ca2Cr2O5 NPs and (b) CaMnO3 NPs.

Figure 6 shows Transmission Electron Microscopy TEM) images of the CaMnO3​ and Ca2​Cr2O5​, (a, b), nanoparticles show a somewhat spherical morphology with an particle size of about 20 nm of CaMnO3​ (a), and 100 nm of Ca2​Cr2O5​, this is an important factor for oil absorption, enhancing compatibility with vehicles.

The SEM of (a) Ca2Cr2O5 NPs and (b) CaMnO3 NPs.

ICP (Inductively Coupled Plasma) Spectroscopy is an analytical technique used to measure and identify elements within a sample matrix based on the ionization of the elements withing the sample.

Table 6 presents the results of the ICP measurements of the samples and suggests that the discrepancy between the measured and calculated metal concentrations in the calcined samples and prepared mixtures may be due to the differing deposition preferences of the calcium ions. Ca ions tend to deposit in an alkaline medium, whereas manganese (Mn) and chromium (Cr) ions are more readily deposited in an acidic medium.

The ASTM measurements of the pigment properties listed in Table 7 revealed the following: Where: T = toluene; E.G., = ethylene glycol; B.A. = butyl glycol; N.B. = normal butanol; M.E.K. = methyl ethyl ketone; L.O.I. = loss on ignition; H = Hagman (fineness unite). We can observe the following results based on the tabulated results in Table 7.

The ASTM measurements of the pigment properties listed in Table 7 revealed the following: T = toluene, E.G. = ethylene glycol, B.A. = butyl glycol, N.B. = normal butanol, M.E.K. = methyl ethyl ketone, L.O.I. = loss on ignition, and H = Hagman (fineness unit). Based on the tabulated results, we can observe the following in Table 7.

The obtained values for the prepared (Ca2Cr2O5 and CaMnO3) NPs ​were slightly alkaline, which is beneficial for resisting the salinity of seawater during microbiofouling test.

Oil absorption is a well-known indicator of whether a pigment will consume binder when applied to paints. More binders will be required to fully wet the pigment and create a homogeneous paint film as the oil absorbs more paint. Table 7 illustrates that calcium-chromium oil absorption was the lowest in the group, while calcium-manganese oil absorption was the highest.

The moisture results of the two prepared mixed metal oxide nanoparticles are very low, indicating a negligible effect of moisture on the weight of the pigment before use in the paint formulation.

Based on the results in Table 7, the degree of fineness for the prepared CaMnO3 and Ca2​Cr2​O5​ was observed to be 8H for Ca2Cr2​O5​ NPs and 7H for CaMnO3​. This indicates that the higher efficiency of results based on Ca2Cr2O5​ is due to its better dispersion in the pigment-vehicle compared to CaMnO3​.

This test method measures the percentage of color produced when the pigment comes into direct contact with various solvents. It is useful as a quick and simple test for the pigment’s overall bleeding properties. The observed results show a high degree of stability for the prepared mixed metal oxide NPs, with Table 7 indicating no bleeding (non-dissoluble color).

This test calculates the pigment weight loss during high-temperature ignition. The results show that the pigment does not change in weight or color when subjected to high temperatures, indicating that the created mixed oxides are incredibly stable under various conditions.

The SEM images of the paint formulation based on F3, which contains CaMnO3 ​and Ca2​Cr2O5​, illustrate that there are no morphological abnormalities in this formulation, as shown in Fig. 7. This is consistent with the pigment-vehicle dispersion of both CaMnO3​ and Ca2​Cr2O5​, suggesting good dispersion. However, it is possible that Ca2Cr2​O5​ was dispersed similarly to CaMnO3 NPs. This aligns with the fineness of grind and oil absorption results reported for both manufactured metal oxide NPs.

SEM images of the paint formula based on CaMnO3 (a) and (b) Ca2Cr2O5 NPs.

As listed in Table 8 and shown in Fig. 8, which represent the mechanical properties and chemical resistance of dry-painted films based on all paint formulations (F1, F2, and F3a, b). From this table, it can be concluded that all painted films have passed the chemical resistance test with no observable changes detected in the samples. At the same time, the recorded results of the mechanical properties of the tested films showed an improvement in impact resistance (1.3–1.9 kg), scratch hardness (1.4 to > 2.2 kg), and adhesion cross-cut (4B-5B) for the dry-painted films of F1 to F3a, b, respectively. This improvement in mechanical properties and chemical resistance for the painted films based on Ca2​Cr2O5​ and CaMnO3 NPs was observed and showed that paint-based mixed metal oxide NPs are more efficient than samples based on F1 and are comparable to paint-based F2 (A.F. commercial sample). This efficiency may be attributed to the presence of protective pigments in nanosized form, which helps achieve high dispersion in the pigment-vehicle mixture, enhancing performance and durability. This can also be attributed to the elastic properties of the two types of polymers used (Gum rosin with vinyl resin), and the integration of Ca2​Cr2O5​ and CaMnO3 NPs into the cavities of gum rosin and vinyl resin can hinder any defects that may lead to damage.

Shows the tested mechanical characteristics such as impact, cross-cut adhesion, and hardness of the coated steel films.

The anticorrosion performance of the paint formulations on the metal surface due to exposure to a saltwater environment was examined using a salt spray test. After testing, the analyzed samples were compared with control panels, and images from the salt spray test are shown in Fig. 9. When these images were analyzed, it was observed that the sheet plates coated with the blank sample (F1) did not show effective anticorrosion performance, failing to protect against corrosion. While there was minimal blistering, rusting increased over time, starting after 200 h and becoming more pronounced by 400 h. In contrast, the coatings based on cuprous oxide as in F2, and those based on the prepared Ca2Cr2​O5​ NPs and CaMnO3 as in F3a and F3b, exhibited higher resistance to corrosion. According to ASTM B117-19, the corroded surfaces were analyzed, and the results related to corrosion failure are presented in Table 9. The failure was evident on the panel coated with F1, but was almost unnoticeable on the coatings that contained the prepared mixed metal oxides as in F3a and F3b, as well as those based on cuprous oxide (F2), after 400 h of exposure. It was observed that the corrosion resistance of the tested paint panels increased compared to the panel coated with F1. However, surface deterioration of the panels coated with cuprous oxide and CaMnO3​ started after 400 h. This improvement in corrosion resistance can be attributed to several factors:

The use of the prepared mixed metal oxide increased the surface hardness and hydrophobicity.

The use of the prepared mixed metal oxide decreased the coating porosity. This reduction effectively prevented the diffusion of Cl- ions into the polymer-coated metal plates, thereby extending the coating’s ability to protect against corrosion for an extended duration.

The presence of the prepared mixed metal oxide NPs and their good dispersion within the gum rosin and vinyl resins resulted in improved adhesion to the substrate, acting as a barrier to isolate mild steel from corrosion. This barrier is impermeable to water and corrosive ions, reducing water permeability.

The long chains in the gum rosin structure made the resin more hydrophobic, reducing water holding power and improving corrosion protection.

The interface between the two resins (gum rosin and vinyl resin) increased the crosslinked network, which acts as an insulating layer that hinders the transport of electrons from the metal surface to aggressive materials necessary for rust formation. Additionally, they act as barriers that slow down the propagation of aggressive species and corrosion products36.

Sometimes, the failure of the coating layer starts when spots or holes form due to aging or mechanical shocks. Aggressive and corrosive materials can then attack the underlying surface through these holes, leading to an increase in exposed area and accelerating the corrosion process. These materials can easily react with the substrate, eventually causing anodic or cathodic delamination. The presence of both resins can form a tough layer that prevents this delamination,26,27,36,37.

Photographic of corrosion resistance of the painted steel panels.

The ability of antifouling paints to prevent fouling organisms from attaching or growing, along with their durability, adhesion, smoothness, and ease of application, is essential for their effective function. Table 3 illustrates an experiment using a vinyl resin matrix. Since mixed metal oxide NPs are commonly included as pigments in many paints, it is crucial to examine how they impact the formulation’s performance. This research primarily focuses on the effect of substituting Cu2O in the formulation with mixed metal oxides. It has been demonstrated that substituting 75% of Cu2​O with the prepared mixed metal oxide NPs resulted in new antifouling paint formulations, as shown in Table 3, based on F3a and F3b. Compared to the commercial formulation containing 40% cuprous oxide as a biocide and antifouling agent (AF), the results of these trials regarding proper pigmentation indicate that the new formulations provide better pigmentation outcomes. Therefore, replacing 75% of the cuprous oxide in dry-painted steel plates with the prepared mixed metal oxide NPs enhances performance and durability, including corrosion resistance. The paint formulation F3 was designed to account for the matrix solution rate, which determines how quickly toxic particles are exposed to seawater. The marine coating systems were exposed to seawater for approximately six months (twenty-four weeks) from January to June 2023 in the Suez Canal (Ismailia, Egypt). The efficiency of the paints was evaluated by visual inspection of macrofouling on the coatings after six months of immersion. The results of anti-microfouling activity during the first weeks of immersion are shown in Fig. 10. Micrographics revealed that steel plates painted with F2 and F3 were efficient against microfouling, similar to those coated with the antifouling formula containing biocide (F2). Based on the investigation and the visual photographs shown in Fig. 8, the following conclusions can be drawn:

Shows the photos of the painted steel plates after immersion in seawater, (a) painted with free antifouling, (b) painted plate without incorporated with metal oxide NPs, (c) painted plate based on Ca2Cr2O5 NPs (d) painted plate based on CaMnO3.

After 8 weeks of immersion in seawater, the painted steel plates based on F1 (free biocide formula) exhibited significant fouling, with the development of homogeneous and thicker fouling films due to the growth of microalgae on the surface. A thick and dense biofilm was observed38. In contrast, no wet weights or settlement were recorded on the painted steel plates based on F2 and F3, which were more efficient against micro biofouling. This effectiveness is attributed to the Cu2​O in F2, which is more resistant to fouling and microorganisms, and the presence of prepared CaMnO3 and Ca2​Cr2​O5 NPs in F3, which also contributed to preventing settlement and growth of macrofouling and enhancing the high durability of the paint.

After 16 weeks of immersion, the fouling covered approximately 100% of the area on the painted steel plates based on F1 (free biocide formula), which were completely fouled. In contrast, the plates based on F2 and F3, particularly those with Ca2​Cr2​O5 NPs, remained more efficient and highly resistant to various types of fouling. The painted steel plates based on F3 (CaMnO3​) showed some settlement and growth of macrofouling but still maintained antifouling activity.

After 18 weeks of immersion, significant antifouling activity was still noted on the painted steel plates based on F2 and F3. However, the plates based on F3 (CaMnO3) NPs showed some settlement and growth of macrofouling. The wet weights of fouling on these substrates were observed, compared with painted plates based on F2 and Ca2Cr2​O5 NPs, which still exhibited significant antifouling activity and were not significantly affected due to the presence of Cu2​O in F2 and metal oxide NPs in F3.

After 24 weeks of immersion, the fouling covered approximately 100% of the painted steel plate F1 area, which was completely fouled. The main biofouling organisms observed included various algae resistant to the coating layer, leading to failure of the coating system and extensive settlement from other fouling organisms. As seen on the painted steel based on F3 (CaMnO3​) NPs only showed slime and a few green algae during the six months of immersion. The painted plates based on F2 and Ca2​Cr2​O5 NPs still demonstrated significant antifouling activity, with no accumulations or settlements recorded, due to the coatings’ hard, smooth surfaces, which limited the adhesion strength of foulants. A significant issue with using Cr and Mn metal oxide NPs as antifoulants is their potential to increase corrosion resistance when applied to steel surfaces, similar to other mixed metal oxide NPs investigated previously as anticorrosive pigments24,37.

The type of biocide was considered when designing three paint formulations: F1, which is a biocide-free paint; F2, a commercial antifouling standard based on cuprous oxide (F3a); and F3b, which is based on CaMnO3​ NPs and uses gum rosin and vinyl resin as binders. These paints are listed in Tables 2 and 3. Tin-free AF paints (F2 and F3) generally have a longer service life due to their ability to slow down the release rate of the binder, which helps prevent biofouling from growing and settling39. Additionally, as part of the antifouling paint mechanism to prevent biofouling adhesion, seawater penetrates the paint matrix, dissolves biocides and co-biocides, and allows other additives to slowly diffuse back into the bulk paint39. Depleted primary biocides, such as Cu2​O or the prepared mixed metal oxide NPs, form a thin layer of leached antifouling paint39. There are two types of paint leaching releases in self-polishing polymers (gum rosin and vinyl resin): early leaching and steady-state leaching39,40,41. Table 2 (F2) shows the elemental composition of copper as the primary biocide in AF paint F2, while Table 3 (F3a and F3b) lists Cr and Mn in F3. The high concentration of Cu indicates the presence of primary biocide compounds (Cu2O) in the AF paints (F2). The high resin levels are influenced by the presence of a high concentration of chloride ions in seawater, which increases the dissolution rate of Cu2​O41. When seawater interacts with cuprous oxide, soluble hydrated Cu(I) chloride complexes are formed. During the hydrolysis process, Cu2+ can replace Cu+ as the primary biocidal species42. Chemical reactions and diffusion processes, including the dissolution of seawater-soluble pigments, binder reactions, and paint polishing, regulate the biocide release rate43. Conversely, the high concentration of chloride ions in seawater does not affect the Ca2​Cr2​O5 and CaMnO3 NPs used, which may impact the consistency of the leached layer in self-polishing antifouling (SPC-AF) paints24,37. This suggests that the polymer matrix retains tiny holes due to the absence of biocides, increasing the paint’s overall wetted area. The leached layer undergoes hydrolysis, changing the binder’s wettability from hydrophobic to hydrophilic44,45. The self-polishing effect of partially reacted binders can occur when exposed to less-reacted paint surfaces due to erosion by streaming seawater. A matrix enhanced with Cu or Cr, Mn, and biocide on less-reactive paint surfaces further prevents marine biofouling from adhering. The antifouling results also, indicated that the incorporation of the prepared mixed metal oxide NPs into coatings enhanced the antifouling performance of the coating by improving the coating hydrophobicity and decreasing the coating elastic modulus46,47,48.

Due to their tiny size, nanomaterials have different characteristics from conventional materials in terms of protection. Recently, mixed metal oxide NPs have gained recognition as powerful reactive anticorrosive pigments. Based on the findings, it can be concluded that the optimal pigment loading in gum rosin and vinyl resin-based paints is 2:1% by pigment volume concentration (PVC). So, the mixed metal oxide NPs were evaluated as biocides in a tin-free, self-polishing antifouling paint., by preparation of Three paint formulations (F1 as a primer without any biocide), F2 (antifouling formulation based on 100% cuprous oxide) and F3 based on 75% Ca2​Cr2O5​ and CaMnO3 instead of cuprous oxide (F3 a, b). All the painted films were tested according to the corrosion resistance and against slime-forming micro biofouling organisms. The results showed that the tested formulations’ corrosion resistance properties and their antifouling agents’ behavior followed, F2 ˃ F3a > F3b > F1. This promising performance result of the prepared paint formulations based on mixed metal oxide NPs can be attributed to several critical factors. First, A lower toxicity for these active substances was revealed comparatively to cuprous oxide, Second, many recent corrosion inhibitors are based on metal oxides, particularly mixed metal oxides, and finally, due to their effectiveness against antimicrobial activity.

Data is provided within the manuscript or supplementary information files.

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Chemistry Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, 11884, Egypt

H. Abd El-Wahab

Department of Chemistry, Faculty of Science, Umm Al-Qura University, Makkah, Saudi Arabia

Hossa F. Al-Shareef

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H. Abd El-Wahab and Hossa F. Al-Shareef, wrote the main manuscript text and prepared figures. All authors reviewed the manuscript.

Correspondence to H. Abd El-Wahab.

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El-Wahab, H.A., Al-Shareef, H.F. Novel antifouling paint formulation based on Ca2​Cr2O5​ and CaMnO3​ NPs as a protective pigment. Sci Rep 14, 24474 (2024). https://doi.org/10.1038/s41598-024-74245-3

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Received: 17 June 2024

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Published: 18 October 2024

DOI: https://doi.org/10.1038/s41598-024-74245-3

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