Additional Energy Input Research Articles

All-Ceramic, compressible and scalable nanofibrous aerogels for subambient daytime radiative cooling

Radiative cooling is a passive cooling technology that radiates heat directly to outer space without any additional energy input and is therefore of great significance in reducing the consumption of energy. However, the radiative cooling in subambient daytime is difficult to implement and usually requires complicated structural designs, such as photonic crystals and metamaterials, which are neither cost-effective nor scalable. Here, we demonstrate that silica-alumina nanofibrous aerogels (SAFAs) synthesized by electrospinning can provide a high solar reflectance of ∼95 % and a high atmospheric window emissivity of ∼93 %, owing to the scattering reflection and selective emission of the fiber network in aerogel. During field tests, the SAFAs remain more than 5 °C below the ambient temperature, theoretically yielding a radiative cooling power of ∼133.1 W m−2. Through scalable manufacturing routes, the SAFAs exhibit high compression fatigue resistance, robust fire resistance and excellent thermal insulation. The low cost and high performance of these SAFAs present great potential for large-scale passive radiative cooling applications.

Harnessing Waste Heat from Indoor lamps for Sustainable Thermocatalytic Mineralization of Acetaldehyde using Platinized TiO2

This study demonstrates the first reported thermocatalytic oxidation of an indoor volatile organic compound (VOC), acetaldehyde, by harnessing the waste-heat energy from indoor light sources (e.g., halogen lamps) without additional energy inputs. With an optimal Pt–TiO2 catalyst, the designed catalyst-coated lampshade was successfully activated under waste-heat energy (∼120 °C) and achieved the complete mineralization of CH3CHO into CO2 (k = 0.02 min−1). The catalytic activity of Pt–TiO2 was extremely dependent on its preparation method which greatly influenced the characteristics (e.g., oxidation state and size) of Pt. The thermocatalytic oxidation mechanism of CH3CHO over Pt–TiO2 was investigated, which revealed that O2 and H2O sources play vital roles. Although Pt is an expensive noble metal, the thermocatalytic process on the Pt–TiO2-coated lampshade without additional energy, along with its outstanding activity, can offset the high material cost. The proposed strategy offers a sustainable and feasible method for the degradation of indoor VOCs.

Scalable and paint-format colored coatings for passive radiative cooling

Passive radiative cooling is an innovative way to radiate heat from objects to outer space by reflecting the sunlight and producing emission in the infrared spectrum especially in the atmospheric transparency window without additional energy input, which has received a widespread attention. However, state-of-the-art radiative coolers have a white appearance in the reflection of the total incoming solar radiation, facing inevitable challenges for anti-glare and other aesthetic issues. To address these problems, we have developed scalable colored coatings by using a facile solvothermal reaction. A combination of color and efficient radiative cooling has, thereby, been achieved by sacrificing a part of the reflections in the visible spectrum. The reflectance in the near-infrared spectrum, and emittance in the atmospheric window, were then maximized to 0.99 and 0.97, respectively. Without the contribution of an additional reflective layer, this type of coating has been found to achieve a sub-ambient temperature drop of 2.31°C (under a solar irradiance of 885 Wm -2 ) and a net cooling power of 68 Wm -2 . Due to the low cost of raw oxide materials, and simple preparation process, the present study has demonstrated a novel potential for large-scale practical applications of colored coatings for passive radiative cooling. • Colored coatings were synthesized, characterized and fabricated. • Attained cooling performance by maximizing near-infrared reflectance and emittance in the atmospheric window. • Achieved color performance through sacrificed partial reflection in visible spectrum. • Exhibited a sub-ambient temperature drop of 2.31°C and a net cooling power of 68 Wm -2 .

Circularity of building materials: A non-discriminating calculation methodology

The energy transition has shifted impacts to materials, their energy use and potential depletion. Especially affected is the building and construction sector, since it is the sector which has the largest consumption of materials. Therefore, it is of utmost importance that materials cycles be closed as well, that they stay within system boundaries, and that we use objective calculation and evaluation methods. If we look at organic or biobased resources, the basic impacts in their flow are obvious and can be characterised fairly simply: they grow on the basis of solar energy at a certain speed and volume per unit of land. It’s a constantly renewing flow, with use maximised to what naturally (re-)grows. In-depth analyses have created growing awareness that non-organic materials are also in fact renewable, even without human intervention but in different scales of time and volume, in time frames way beyond the normal planning horizons of humans. They are renewed by volcanic and tectonic movements of the Earth’s crust. The paper explores how non organic materials will renew, that is, become re-concentrated in the Earth’s crust. In fact it is the concentration that is crucial for effective use, without additional energy input that would deplete other sources. From this analysis it follows that all resources can be characterised by the speed and volume in which they concentrate—either by the soil and solar route, or by the Earth movement route. : “Resources can thus be grouped into four categories: regrowable, streaming, slow and synthetic. The characterisation shows a similar pattern in other indicators for these resources: the slower the resources are regenerated, the more (embodied) energy required to obtain the resources, for instance. This is an attempt, a pre-study, to set up a methodology, and the first estimations for the global flows of resources in different categories. In the end it turns out that all resources have a natural renewal basis, and that there are no sustainable or non-sustainable (or non-renewable) resources: it is their use, within maximised flows, that determines their sustainability. It requires that we re-define the notion of ‘circular’.

The split-belt rimless wheel

Split-belt treadmill walking, in which the two belts move at different speeds, reveals a mechanism through which energy can be extracted from the environment. When a person walks with positive step length asymmetry on a split-belt treadmill, the treadmill can perform net positive work on the person. Here we use a split-belt rimless wheel model to explore how people could take advantage of the treadmill. We show that a split-belt rimless wheel can passively walk steadily by capturing energy from the treadmill to overcome collision losses, whereas it loses energy on each step with no way to recover the losses when walking on tied belts. Our simulated split-belt rimless wheel can walk steadily for a variety of leg angle and belt speed combinations, tolerating both speed disturbances and ground height variability. The wheel can even capture enough energy to walk uphill. We also built a physical split-belt rimless wheel robot and demonstrated that it can walk continuously without additional energy input. In comparing the wheel solutions to human split-belt gait, we found that humans do not maximize positive work performed by the treadmill. Other aspects of walking, such as costs associated with swing, balance, and free vertical moments, likely limit people’s ability to benefit from the treadmill. This study uses a simple walking model to characterize the mechanics and energetics of split-belt walking, demonstrating that energy capture through intermittent contact with two belts is possible and providing a simple model framework for understanding human adaptation during split-belt walking.

Siphon-driven interfacial photocatalytic reactors enhanced by capillary flow for continuous wastewater treatment

Catalytic membrane reactors based on photo-Fenton reactions have been widely applied in organic wastewater treatment. Conventional porous membrane reactors require a multi-cycle operation to achieve a high degradation efficiency. To realize the continuous treatment of wastewater with high efficiency, we propose a novel siphon-driven interfacial photocatalytic reactor based on the β-FeOOH-coated fabrics in the current work, in which the feed transport is within the fabric rather than across the fabric. The liquid flow is driven by gravity without additional energy input and can be adjusted by the structural parameters to match the reaction rate. Moreover, the confined capillary flow ensures sufficient contact between the feed and catalysts, as well as sufficient sunlight utilization, leading to the high degradation efficiency (>99 %) for a variety of organic contaminants such as tetracycline and dyes. The relationship between the fabric structural parameters and degradation performance was also investigated to achieve an optimal design.

Approaches Towards Improving Zinc-Nickel Batteries Performance

The zinc/nickel electrochemical system has long been proposed as a good candidate of secondary alkaline batteries due to its excellent performance versus other aqueous batteries, such as high practical specific energy, excellent specific power, high open circuit voltage, low cost and low toxicity [1,2]. These advantages make it suitable for replacing lead-acid and nickel-cadmium batteries [3]. However, the high solubility of zinc in concentrated alkaline electrolytes is still a significant problem that induces two main failure mechanisms: a shape-change of the zinc electrode and a redistribution of the zinc active material due to its dissolution/redeposition during cycling. Dendritic growth can occur as a consequence of zinc dissolution/redeposition, and if severe, may lead to separators’ perforation and internal electrical short-circuits [4]. These drawbacks reduce the cell's capacity and lifetime, especially compared to traditional competing systems [5]. In addition, since the hydrogen evolution reaction (HER) is thermodynamically possible (especially during charging), the coulombic efficiency of the zinc electrode can be lowered by this parasite reaction [6]. The undesirable HER consumes water and some of the active material, yielding zinc hydroxide which in turn can generate a passivation layer that lowers the usability of the zinc anode materials [7]. There are different approaches to overcome these problems, such as the integration of additives in the active material formulation and/or in the electrolyte.In this contribution, we will show how regeneration of the active material can be obtained via appropriate steps of rest submitted to the active material and without the need for additional energy input. The so-called “self-healing” of the active material allows to recover a substantial part of the electrochemical performance. The concept was deeply studied and monitored by scanning electron microscopy coupled with elemental mapping by X-ray energy dispersive spectrometry, and operando tomography. An increase in the coulombic efficiency has been demonstrated making this discovery very promising for the future of zinc-based alkaline batteries. Keywords: Zinc-nickel batteries, additives, self-healing

Bioimaging Applications of Excitation-Independent Fluorescence Carbon Dots

Carbon dots (CDs) were synthesized via a simple method and applied in bioimaging. The CDs display excitation-independent fluorescence emission and exhibit upconversion PL, providing further tissue penetration and greater sensitivity as the effect of the autofluorescence of biological bodies is minimized and cellular imaging. This is the first time that excitation-independent carbon dots is prepared via a truly facile approach without the need of external heating or additional energy input. These results indicate that the CDs have excellent potential to be applied in biomedical and clinical analysis.

Hydrothermal carbonization processes applied to wet organic waste streams

Various organic waste streams are generated daily by human activities such as municipal, agricultural and industrial. The sustainable disposal of these organic wastes is a serious societal challenge. When the disposal process is not efficient, this type of wastes creates important pollution risks for air, soil, underground water and sea. Especially, wastes that have high moisture content cannot be eliminated cost effectively via thermo-chemical conversion by conventional processes such as pyrolysis, gasification and combustion. These processes necessitate the pre-drying of wet wastes which require additional energy input and increase the operational costs. One promising approach for the management and valorization of highly wet waste streams is the use of hydrothermal technologies. Hydrothermal carbonization is a very appropriate approach for valorizing wet organic wastes using water as a medium at high temperature and pressure under subcritical conditions. The generated “hydrochar” is a solid lignite like material that can be used for energy generation (by gasification or combustion) but also for environmental practices such as soil remediation and carbon fixation. This review focuses on the feedstock potential of wet organic wastes of sewage sludge, food wastes, various animal manure and macroalgae, and their valorization by hydrothermal carbonization. Structural, physical and energy conversion characteristics of hydrochars produced from various wet organic wastes are compared and discussed. Usage areas of hydrochars are also assessed.

Eliminating the need for anodic gas separation in CO2 electroreduction systems via liquid-to-liquid anodic upgrading

Electrochemical reduction of CO2 to multi-carbon products (C2+), when powered using renewable electricity, offers a route to valuable chemicals and fuels. In conventional neutral-media CO2-to-C2+ devices, as much as 70% of input CO2 crosses the cell and mixes with oxygen produced at the anode. Recovering CO2 from this stream adds a significant energy penalty. Here we demonstrate that using a liquid-to-liquid anodic process enables the recovery of crossed-over CO2 via facile gas-liquid separation without additional energy input: the anode tail gas is directly fed into the cathodic input, along with fresh CO2 feedstock. We report a system exhibiting a low full-cell voltage of 1.9 V and total carbon efficiency of 48%, enabling 262 GJ/ton ethylene, a 46% reduction in energy intensity compared to state-of-art single-stage CO2-to-C2+ devices. The strategy is compatible with today’s highest-efficiency electrolyzers and CO2 catalysts that function optimally in neutral and alkaline electrolytes.

Efficient destruction of humic acid with a self-purification process in an Fe0-FeyCz/Fex-GZIF-8-rGO aqueous suspension

Natural organic matter (NOM) has diverse negative impacts on water purification, however, preventing them occurrence very difficult. Herein, humic acid (10 mg/L), as the main component of NOM, is completely destructed within 120 min in the Fe0-FeyCz/Fex-GZIF-8-rGO air-saturated aqueous suspension without additional energy input, while its mineralization is followed by three kinetic constants within 480 min. During the process, HA was first complexed with Fe0-FeyCz/Fex-GZIF-8-rGO by π-π interaction and H-bonding interaction and cleaved to aromatic compounds and then to alkanes and alcohols with some small acids before 120 min. The electron paramagnetic resonance (EPR) analysis and density functional theory (DFT) calculations confirmed that a strongly polarized alkane-alcohol complex was formed after 150 min with an electron-rich hydroxyl group area in alcohol and an electron-poor alkane area. Moreover, the more electrons of alkane in the complex are delocalized and trapped by O2, with the adsorption of the alkane-alcohol complex on the catalyst surface based on the analyses of both electrochemical impedance spectroscopy (EIS) and chronoamperometry, greatly promoting the surface cleavage and hydrolytic process of alkane in the complex and producing more •OH for pollutant degradation than it does from the HA surface complex, which results in the highest mineralization rate in the period of 150–390 min. Our findings demonstrated that the current system is very promising for complex mixture-containing water purification without additional energy.

Internal instability of thin-walled beams under harmonic moving loads

Frequent resonance may result in excessive vibrations and endanger the safety of bridges. Firstly, the governing equations of motion are derived for the vertical, lateral and torsional vibrations of a mono-symmetric thin-walled box beam under a harmonic moving load. Then the resonance conditions are derived by letting the denominator of the response of concern equal to zero. For the mono-symmetric beam, the vertical resonance is uncoupled, but the torsional and lateral resonances are coupled. When in vertical resonance, the vertical motion of the beam will diverge by growing to a maximum during the acting period of the moving load. Similar phenomenon exists for the torsional–flexural resonance. A specific case occurs when the above two resonance frequencies coincide, for which the critical length of the beam can be determined. The phenomenon of simultaneous resonance is a kind of internal instability featured by the fact that the beam can transform repetitively from the vertical mode to the torsional–flexural mode, and vice versa, with no additional energy input. To avoid the inherent internal instability, a beam should be designed with a length not equal or close to the critical length presented in this paper. All the aforementioned resonances have been extensively studied for cases involving both harmonic and random moving loads and validated by the finite element analysis.

A robust PVA/C/sponge composite hydrogel with improved photothermal interfacial evaporation rate inspired by the chimney effect

Solar-driven interfacial evaporation has attracted significant research attention owing to its high conversion efficiency of solar energy and transformative industrial potential. The evaporation rate depends on the intrinsic properties of the photothermal conversion materials and external environmental factors. The development of a photothermal evaporation device with a high evaporation rate is urgently required for the application of photothermal interfacial evaporation. Here, we introduce a chimney in a hydrogel composite material to create a novel photothermal evaporation device. First, we fabricated a hydrogel composite material by in situ polymerization in the sponge. The porous structure of the sponge endows the resulting composite hydrogel with a high water-absorption rate. Thus, it improves the water supply rate of traditional hydrogel materials. Meanwhile, we applied a 26 cm high chimney to the photothermal evaporation device and demonstrated that the evaporation rate highly increased from 1.56 to 5.90 kg m−2 h−1 for pure water evaporation, 1.43 to 4.47 kg m−2 h−1 for seawater evaporation under 1 sun illumination. The evaporation system requires no additional energy input or other external conditions. In addition, the improved device structure is simple and can be applied to previously reported photothermal evaporation systems to achieve a higher evaporation rate.

Increasing energy efficiency of counter-rotating wind turbines by experimental modelling

With the significant advance in exploiting wind energy, there has been a shift in research from the study of conventional systems to the study of counter-rotating systems due to additional energy input of the second rotor. The paper presents the results of the research on achieving an increase in the energy efficiency of counter-rotating wind power conversion systems. For this purpose, there have been designed different sizes of wind rotors, were 3D printed and tested in an open-circuit aerodynamic tunnel for different wind velocities and axial distances between rotors. The constructive design consisting of a smaller diameter front rotor and a larger rear rotor was chosen. The individual wind rotors were used to configure two experimental models of counter-rotating wind systems. The testing results analysis and interpretation enabled the establishing of the design and operating conditions that provide the highest power extracted from wind at 10 m/s velocity. A higher efficiency of the wind turbine system is achieved for a lower ratio between the front and rear turbines. In the case of the analysed experimental models, an increase in system efficiency of 49.14% is achieved for a 0.845 diameter ratio, and of 39.02% for 0.945 diameter ratio, respectively.

Taxonomical Investigation of Self-Sufficient Kinetic Building Envelopes

Currently, most descriptions of low-energy buildings assume that the envelope acts as a barrier against energy loss. However, this approach does not focus on the potential exploitation of favorable contributions from the surrounding environment that could lead to additional improvements in performance. Adaptive building envelopes (ABEs) offer a number of different options for this. However, many of them require the supply of a certain energy amount to operate. A viable alternative is offered by self-sufficient solutions that adopt responsive materials-based actuators, which are capable of modifying some of their properties in response to environmental stimuli (e.g., temperature, humidity, light, and others), which determines the dynamic behavior of the envelope without requiring additional energy inputs and minimizing technical complexity. The research field into self-sufficient adaptive envelopes (SSAEs) has received a significant boost recently. Given the heterogeneity of the proposed solutions, this paper will report on a taxonomical investigation that will be performed on the available studies that deal with SSAEs, which highlight their role in innovation and will provide a systemic classification for applications to support future research.

Experimental evaluation of a thermosyphon-based waste-heat recovery and reintegration device: A case study on low-temperature process heat from a microbrewery plant

An experimental study was conducted to design, build and test the performance of a waste-heat recovery device. Its feasibility and performance were evaluated, based on its implementation within a brewing process; recovering unallocated residual energy from wort cooling water (40 °C to 80 °C) and using it to heat cool air for barley drying (32 °C to 48 °C). Given the quality associated to the low-temperature source, thermosyphons were selected as heat conveyance device. The proposed heat recuperator design uses 18 carbon-steel thermosyphon tubes filled with a mixture of distilled water and hydrazine hydrate, as corrosion inhibitor, at 20% of the total inner volume. Given the passive nature of the device, the length ratio between the evaporation and condensation zones was also analysed, ranging from 50:50, 40:60 and 30:70. The results showed that the 50:50 length ratio was the most disadvantageous configuration available, with the lowest efficiency and heat conveyance, ascribed to a higher radial heat flux into the evaporator, thus, reducing the operation range considerably. Meanwhile, increasing condenser length, 40:60 and 30:70 length ratios, yields a higher maximum condensation heat flow, with 4.15 KW and 4.22 KW, respectively, a 31% increase. However, given the 1.2% difference between them, said increase is comparatively negligible, entailing that, for this thermosyphon setup, peak heat transfer available is reached with the 40:60 length ratio. Regarding efficiencies, it was found that the 50:50 length ratio is particularly susceptible to the thermosyphon inherent operation limits, specifically, the boiling limit. Nonetheless, all configurations have efficiencies above 50% with heat flows above 1.5 KW. Additionally, it was found that the lowest air flow velocities yield the highest achievable efficiencies, with 84%, 98% and 94%, for the 50:50, 40:60 and 30:70 length ratios respectively. Similarly, when evaluating through the thermal capacity framework, it was found that the 50:50 length ratio only possess a 8% accomplishment rate, whilst the remaining configurations, increase said rate by 20%. However, it also shows that the 30:70 length ratio yields a more dispersed dataset, which reveals that the imbalance after surpassing peak heat transfer, renders the device more susceptible to both inherent and environmental effects. From the findings it was found that the proposed device, with a 40:60 length ratio is capable of successful recover and reintegration of residual energy, without modifying existing brewhouse installation or requiring additional energy input. Therefore, the general assessment conducted proposes thermosyphon-based heat exchangers as viable alternatives for low-temperature heat recuperation beyond the case study here discussed.

Performance of a shallow solar pond coupled with a heat pump cycle for thermal energy in net zero-energy buildings

Refrigerant evaporation, in heat pumping systems, is a particularly complex process. Since the evaporator is subjected to environmental conditions, several factors weigh in on overall system performance, mainly, the additional energy input from the surroundings. This renders the evaporation process especially susceptible to gaps and fluctuations of said energy availability, particularly in solar-assisted setups. Despite the, comparatively, high heat flux associated to this source, these occurrences make them suitable mostly for low-to-medium thermal requirements, especially in regions with more extreme climates. The present work introduces a novel evaporator design, based on solar ponds. The proposed evaporation device incorporates a short-term, passive, thermal storage solution to compensate for gaps in energy availability. A mathematical-thermal model is developed and a performance assessment is conducted based on real seasonal atmospheric and operation conditions. For this study R134a, R152a, R1234yf and R1234ze(E) were used as working fluids. The proposed heat pump configuration is evaluated for hot water production at 55 °C, indoor air heating at 18–22 °C and a combined simultaneous scheme. The results show that this configuration performs well under moderate climate conditions. For hot water production during spring, highest outlet temperature of 68.54 °C for the R1234yf working fluid, were reached and maintained after the first 13 h. Internal thermal capacitor reached an average temperature of 61.88 °C for R1234yf. During winter, these temperatures decrease almost by a third, with 40.6 °C for R1234yf working fluid. However, daily average outlet temperature of 64.8°Care reached within the first 15 h of operation. Despite a lower thermal storage, with average capacitor, the system yielded consistent average outlet temperature of 20.7 °C. For a simultaneous operation scheme, desired outlet water temperature, is reached within the first 16 h of operation, whilst the indoor air temperature reaches comfort levels within the first 12 h. Despite employing part of the energy absorbed to maintain a stable comfort condition within the dwelling, instead of compensating the heat loss of the hot water tank, both goals are achieved. The inclusion of an inner thermal capacitor that collects and stores energy at a much higher rate provides the refrigerant with an additional heat source. This results in a more effective overall energy absorption of the evaporator, which exceeds the rate at which heat is dissipated from the tank/dwelling to the environment. This heat loss buffer lessens, considerably, the thermal demand during periods with lower energy availability, resulting in achievable outlet conditions.

Chainlike Structure Formed in Iodine Monochloride Graphite Intercalation Compounds

The structure of iodine monochloride (ICl) intercalated into graphite (GIC) has been revisited, and a stage 1 stoichiometry of about 10 carbon atoms to 1 ICl molecule is determined. Intercalation proceeds readily at room temperature without additional energy input. A chainlike structure of alternating halogen species is proposed for the intercalation layer based on detailed Raman spectroscopic analysis and ab initio calculations. Long-range ordering is observed, reaching beyond one layer of carbon. The calculated density of states shows p-doping of the carbon layers upon intercalation, in agreement with Raman spectroscopic analysis. The intercalation is reversible upon heating and can be cycled several times. While iodine chains have been observed in other nanocarbons, ICl is the first example of extended halogen chains intercalated in graphite. Indeed, intercalant phases of acceptor GICs have rarely been studied to date, and the current findings are of potential interest in structural chemistry, materials science, solid-state batteries, and other areas.

Water harvesting from desert soil via interfacial solar heating under natural sunlight

Freshwater crisis seriously challenges human survival and development, especially in arid regions. Solar-driven interfacial evaporation has recently received tremendous interest for collecting clean water, yet is only feasible in regions with available surface water. Atmospheric water harvesting is independent of surface water but requires high RH, additional energy input and complex equipment. Here, we demonstrate efficient water harvesting from desert soil in very dry regions (air RH < 10%, soil moisture content < 3%) via interfacial solar heating under natural sunlight. The water harvesting device, composed of merely a thin layer of activated carbon (for interfacial solar heating on soil surface), a commercially available polyethylene film (for vapor condensation and water transport) and a water container, could collect 1.13 kg of clean water per square meter of desert soil per day (8 h), i.e., 0.53 kg of clean water per kilogram of activated carbon per hour, under a solar flux of 0.26–0.55 kW m−2. Besides, the soil water harvesting system is very portable, low-cost and scalable. This work opens up a new sustainable approach for solving the freshwater crisis in arid and impoverished regions.

Toward enhanced catalytic activity of magnetic nanoparticles integrated into 3D reduced graphene oxide for heterogeneous Fenton organic dye degradation

Composite Fenton nanocatalyst was prepared by water-based in situ creation of Fe3O4 nanoparticles integrated within the self-assembly 3D reduced graphene oxide (rGO) aerogel. The hybrid applied for the degradation of Acid Green 25 (AG-25) organic dye in an aqueous solution, in the presence of H2O2. By investigating the conditions that maximize the dye adsorption by the 3D composite, it was found that the pH of the solution should be adjusted between the pKa of the functional groups present on the rGO surface (carboxylic acid) and that of the dye (sulfonic acid) to promote electrostatic interactions dye—3D structure. Performed under these conditions, Fenton degradation of AG-25 in presence of H2O2 was completed in less than 30 min, including all the intermediate products, as demonstrated by MALDI–TOF–MS analysis of the aqueous solution after discoloration. Moreover, this was achieved in a solution with as high a dye concentration of 0.5 mg/mL, with only 10 mg of 3D composite catalyst, at room temperature and without additional energy input. The high performance was attributed to the creation of charge-transfer complex between rGO and Fe3O4 nanoparticles throughout covalent bond C–O–Fe, the formation of which was promoted by the in situ synthesis procedure. For the first time, up to the authors’ knowledge, AG-25 degradation mechanism was proposed.