Phosphate Immobilization in Wastewater Using MgO-Modified Industrial Hemp-Stem-Driven Biochar.

[NNadir]

The paper I'll discuss in this post is this one: Strong Immobilization of Phosphate in Wastewater onto the Surface of MgO-Modified Industrial Hemp-Stem-Driven Biochar by Flowerlike Crystallization

One almost cannot be a member of my generation without having a generalized knowledge of the effects of marijuana use, which I oppose. Before everyone jumps down my throat - this happens quite a bit - this does not mean that I support criminal sanctions against marijuana, but I oppose its use, and to be frank, its open sale in the equivalent of liquor stores.

Over the years, of course, I've heard all kinds of arguments about why marijuana is good for this or that, some arguments being quite tortured frankly, but one hears them anyway. I generally don't buy them; and I've generally been dismissive of all of them.

One of the more tortured arguments I've heard - thankfully far less so recently - since I spend a lot of time thinking about climate change, is that hemp is the key to removing carbon dioxide from the air, more hemp, less climate change.

Sigh...

The world's "bad boy and bad girl" fascination with marijuana of course, has indeed, despite my distaste for the subject, resulted in some very good science however. Notably, this is true of the elucidation of the cannabanoid receptor system, which has implications far beyond their psychological effects.

For a nice brief discussion of areas of interest in this receptor system, there is in a paper about a privileged structure acting upon it, an introduction giving an overview. It's this paper: Polycyclic Maleimide-based Scaffold as New Privileged Structure for Navigating the Cannabinoid System Opportunities (Alessandra Bisi*Alessandra Bisi , Alì Mokhtar Mahmoud, Marco Allará, Marina Naldi, Federica Belluti, Silvia Gobbi, Alessia Ligresti*, and Angela Rampa* ACS Med. Chem. Lett. 2019, 10, 4, 596–600) The introduction discussing the cannabanoid systems "opportunities" is this:

The presence of an endogenous cannabinoid system (ECS) was discovered while attempting to understand the effects induced in humans by the use of Cannabis Sativa.(1) It has now become clear that ECS dysregulation is connected to pathological conditions, and thus, its modulation has gained enormous potential for intervention in multiple areas of human health. ECS is a neuromodulatory system found both in the brain and in the periphery. It consists of two G protein-coupled receptors, known as the cannabinoid type 1 (CB1) and type 2 (CB2) receptors, endogenous ligands, of which anandamide (N-arachidonoyl-ethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) are the best characterized, and the enzymes that regulate their production and degradation.(1) The CB1 receptors (CB1Rs) are primarily located in the central nervous system (CNS) and represent a therapeutic target that may impact pathways that mediate pain, hunger, neurodegenerative disorders, and drug-seeking behavior, even if detrimental side effects, including psychoactivity, depression, and suicidal thoughts, could be observed. On the contrary, the CB2 receptors (CB2Rs) are mainly distributed in peripheral tissues and immune cells, and therefore, they play significant roles in pathologies involving an inflammatory component (such as pain, inflammatory bowel disease, atherosclerosis, osteoporosis, and cancer).(2) In particular, with respect to cancer, pharmacological activation of the CB2R has been shown to produce antitumor effects in different cancer types. Changes in the expression of this receptor were reported in human cancers and a correlation between its expression, histologic grade, and prognosis has been demonstrated in breast cancer,(3) glioma, hepatocellular carcinoma, pancreatic cancer, endometrial carcinoma, and leukemia.(4?6)

However, the presence of CB2-positive cells in the brain during injury and in inflammatory neurodegenerative disorders might provide a novel strategy for cannabinoid-mediated intervention against stroke-induced neurodegeneration, without the unwanted psychoactive effects related to CB1R stimulation.(7) CB2Rs are also detected in glial cells, and in particular, they are overexpressed in A? plaque-associated microglia, suggesting a crucial role in Alzheimer’s disease (AD).(8) Indeed, several studies have shown that A?-mediated activation of microglia induces the production of various proinflammatory mediators that cause neuronal dysfunction and cell death, suggesting its involvement in AD.(9)...

God bless the memory of Jerry Garcia, I guess...

The paper under discussion here - NNadir should be made to eat his words as often as is possible according to some people (to whom, regrettably, I can't listen owing to the expansion of my wonderful "ignore list" here - is about how hemp can participate in addressing a problem that really, really, really troubles me, the implications of the phosphorous cycle, a cycle which is decidedly not closed, but will need to be so in a sustainable world. It's a very serious matter.

P (phosphate) is a nonrenewable resource, which is also one of the necessary nutrients for the growth of organisms in an aquatic environment. However, excessive phosphorus in surface water will cause water eutrophication and other environmental problems, which have a huge negative impact on the aquatic ecosystem.(1) Therefore, the development of an effective and environmentally friendly method to remove and recycle phosphate from aquatic ecosystems will not only protect the water body but provide a new method for the sustainable development of phosphorus.(2)
Biological,(3) chemical,(4) ion exchange, and adsorption(5) treatment methods have commonly been used for phosphate removal. Biological processes, including activated sludge(6) and biofilm(7) techniques, are widely adopted in many countries. However, due to the sensitivity of microorganisms to water qualities,(8) including temperature and pH, this method shows limited phosphate adsorption efficiency within ?30%. Chemical precipitation and flocculation(9) are common physical–chemical processes, which have an outstanding capacity for phosphorus removal. However, large amounts of chemical sludge and byproducts have also been produced simultaneously. The ion-exchange method applies a strong anion-exchange effect to the selective removal of phosphate, but resin is often easy to poison.(10) Compared with these methods, adsorption has been considered a promising technique, because it provides higher treatment efficiency and a faster removal rate.(11) The common adsorbents, such as biomass,(12) zeolite,(13) hydrotalcite,(14) hydrogel,(15) and montmorillonite,(16) have been used in experiments. Nowadays, biochar is an eco-friendly potential adsorbent due to various beneficial properties, low cost, abundance, lower pollution, and the possibility of regeneration.(17)

Biochar is a carbon-rich solid formed by pyrolysis of biomass wastes at relatively low temperatures under limited oxygen. A large specific surface area, abundant pore structure, and considerable functional groups are the basis of biochar as a potential adsorbent for pollutant remediation. Unfortunately, the surface of biochar with permanent electronegativity has limited phosphate adsorption capacity, so it is of great significance to modify the biochar for enhancing its adsorption efficiency. Recently, various modification methods have been investigated, such as cationic surfactant modification, metal ion surface modification (magnesium,(18) aluminum,(19) calcium,(20) and so on), and rare-earth metal modification (lanthanum,(21) zirconium(22)). However, compared with those of the other two modification methods, metal ion surface modification has a stronger adsorption ability and larger adsorption capacity. Yao et al. obtained MgO nanoparticles derived from anaerobically digested sugar beet tailings, which showed that the maximum adsorption capacity was 133 mg/g.(23) Ming Zhang et al. used porous MgO/biochar nanocomposites to remove phosphate and used Langmuir adsorption capacities as high as 835 mg/g for phosphate...(24)

...However, the phosphate is easily separated from the adsorbent surface due to the unstable structure after adsorption. Therefore, it will be of great importance for the stable immobilization of PO43– in wastewater.

In this work, the Mg PO4)y·zH2O crystallization effect has been used for stably anchoring the adsorbed P onto the biochar surface, which has been paid little attention, as before. Specifically, the biochar was driven from an industrial hemp plant waste by pyrolysis at relatively mild conditions...

The following cartoon shows how the authors make their MgO impregnated hemp stem biochar:



The caption:

Figure 1. Preparation process of MgO/biochar.

Different conditions utilized and the effect on phosphate uptake efficiency are shown in the following table:



The MgO impregnated biochar was characterized by TEM (transmission electron microscopy), XRD(X-Ray Diffraction) , IR (Infrared Spcectroscopy, BET (the Brunauer–Emmett–Teller method for surface area using N2 gas), and SEM (Scanning Electron Microscopy.)

XRD and IR of two samples:



The caption:

Figure 2. (a) XRD of A-C-1 and A-C-2 and (b) FTIR of A-C-1 and A-C-2.

The effect of pH on absorption:



The caption:

Figure 3. (a) Effect of initial pH on the removal of phosphate (C0 = 300 mg/L, at dosage = 1 g L–1, time = 12 h). (b) Equilibrium pH after adsorption of phosphate.

Adsorption science is generally viewed, in a number of applications, by certain kinds of plots, one of which, that Langmuir parameter having earned Irving Langmuir the Nobel Prize. These plots are called "isotherms":



The caption:

Figure 4. Isotherm sorption models for phosphate at different temperatures: (a) Langmuir isotherm and (b) Freundlich isotherm.

Kinetics:



The caption:

Figure 5. Adsorption kinetics for 300 mg/L phosphate on MgO/biochar at different temperatures: (a) pseudo-first-order kinetics model, (b) pseudo-second-order kinetics model, and (c) intraparticle diffusion model.

Some images:



The caption:

Figure 6. (a) SEM of MgO/biochar. (b, c) TEM of MgO/biochar. (d) SAED of MgO/biochar. (e–g) Mapping of Mg, O, and C. (h) EDS of MgO/biochar.

The caption:

Figure 7. (a, d) SEM of MgO/biochar after adsorption. (b, c, f, i, l) Mapping of MgO/biochar after adsorption. (e, g, h, k) TEM of MgO/biochar after adsorption. (j) EDS of MgO/biochar after adsorption.

Changes after adsorption of phosphate:



The caption:

Figure 8. (a) XRD and (b) FTIR of MgO/biochar before and the after adsorption.

A cartoon about how the process works.

Figure 9. Mechanism of phosphate immobilization and the formation process of the flowerlike crystalline compound.

Some remarks from the conclusion:

MgO-modified industrial hemp-stem-driven nanocomposites produced by in situ precipitation have the superior ability to immobilize phosphate from wastewater under a range of pH values and competitive ion conditions. Different carbonization conditions can affect the specific surface area of biochar and the crystallinity of the MgO crystal, and this further affected the phosphate adsorption capacity. Biochar with the large specific surface area provided a good carrier for MgO, which was more conducive to phosphate immobilization by forming the Mg PO4)y·zH2O crystal. The maximum phosphate adsorption capacity was 233 mg/g with the Langmuir model at 25 °C, which outperformed many other adsorbents. Phosphate adsorption was feasible and spontaneous through the study of thermodynamics and kinetics. MgO/biochar had a good reusability, and there was still a 90 mg/g absorption capacity after five cycles. Phosphate removal was mainly controlled by electrostatic adsorption, crystallization, and the inner-sphere surface complex. In conclusion, MgO/biochar was a promising adsorbent for phosphate removal, with a high adsorption capacity and the cost of hemp, as an agricultural waste, being low.

OK, OK, OK...After many decades of hearing about the wonders of pot/hemp/weed/whatever, this potentially represents an important use for the stuff.

I still don't recommend smoking the stuff. It's not good for you.

Biochars, by the way, represent sequestered carbon, perhaps trivial in this application, but it is carbon removed from air.

I trust you're having a safe and enjoyable Sunday afternoon.